Re: [PATCH v2] Persistent grant maps for xen blk drivers
From: Konrad Rzeszutek Wilk
Date: Mon Oct 29 2012 - 10:09:59 EST
On Wed, Oct 24, 2012 at 06:58:45PM +0200, Roger Pau Monne wrote:
> This patch implements persistent grants for the xen-blk{front,back}
> mechanism. The effect of this change is to reduce the number of unmap
> operations performed, since they cause a (costly) TLB shootdown. This
> allows the I/O performance to scale better when a large number of VMs
> are performing I/O.
>
> Previously, the blkfront driver was supplied a bvec[] from the request
> queue. This was granted to dom0; dom0 performed the I/O and wrote
> directly into the grant-mapped memory and unmapped it; blkfront then
> removed foreign access for that grant. The cost of unmapping scales
> badly with the number of CPUs in Dom0. An experiment showed that when
> Dom0 has 24 VCPUs, and guests are performing parallel I/O to a
> ramdisk, the IPIs from performing unmap's is a bottleneck at 5 guests
> (at which point 650,000 IOPS are being performed in total). If more
> than 5 guests are used, the performance declines. By 10 guests, only
> 400,000 IOPS are being performed.
>
> This patch improves performance by only unmapping when the connection
> between blkfront and back is broken.
>
> On startup blkfront notifies blkback that it is using persistent
> grants, and blkback will do the same. If blkback is not capable of
> persistent mapping, blkfront will still use the same grants, since it
> is compatible with the previous protocol, and simplifies the code
> complexity in blkfront.
>
> To perform a read, in persistent mode, blkfront uses a separate pool
> of pages that it maps to dom0. When a request comes in, blkfront
> transmutes the request so that blkback will write into one of these
> free pages. Blkback keeps note of which grefs it has already
> mapped. When a new ring request comes to blkback, it looks to see if
> it has already mapped that page. If so, it will not map it again. If
> the page hasn't been previously mapped, it is mapped now, and a record
> is kept of this mapping. Blkback proceeds as usual. When blkfront is
> notified that blkback has completed a request, it memcpy's from the
> shared memory, into the bvec supplied. A record that the {gref, page}
> tuple is mapped, and not inflight is kept.
>
> Writes are similar, except that the memcpy is peformed from the
> supplied bvecs, into the shared pages, before the request is put onto
> the ring.
>
> Blkback stores a mapping of grefs=>{page mapped to by gref} in
> a red-black tree. As the grefs are not known apriori, and provide no
> guarantees on their ordering, we have to perform a search
> through this tree to find the page, for every gref we receive. This
> operation takes O(log n) time in the worst case. In blkfront grants
> are stored using a single linked list.
>
> The maximum number of grants that blkback will persistenly map is
> currently set to RING_SIZE * BLKIF_MAX_SEGMENTS_PER_REQUEST, to
> prevent a malicios guest from attempting a DoS, by supplying fresh
> grefs, causing the Dom0 kernel to map excessively. If a guest
> is using persistent grants and exceeds the maximum number of grants to
> map persistenly the newly passed grefs will be mapped and unmaped.
> Using this approach, we can have requests that mix persistent and
> non-persistent grants, and we need to handle them correctly.
> This allows us to set the maximum number of persistent grants to a
> lower value than RING_SIZE * BLKIF_MAX_SEGMENTS_PER_REQUEST, although
> setting it will lead to unpredictable performance.
>
> In writing this patch, the question arrises as to if the additional
> cost of performing memcpys in the guest (to/from the pool of granted
> pages) outweigh the gains of not performing TLB shootdowns. The answer
> to that question is `no'. There appears to be very little, if any
> additional cost to the guest of using persistent grants. There is
> perhaps a small saving, from the reduced number of hypercalls
> performed in granting, and ending foreign access.
>
> Signed-off-by: Oliver Chick <oliver.chick@xxxxxxxxxx>
> Signed-off-by: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> Cc: <konrad.wilk@xxxxxxxxxx>
> Cc: <linux-kernel@xxxxxxxxxxxxxxx>
> ---
> Changes since v1:
> * Changed the unmap_seg array to a bitmap.
> * Only report using persistent grants in blkfront if blkback supports
> it.
> * Reword some comments.
> * Fix a bug when setting the handler, index j was not incremented
> correctly.
> * Check that the tree of grants in blkback is not empty before
> iterating over it when doing the cleanup.
> * Rebase on top of linux-net.
It looks good to me. Going to stick it on my for-jens-3.8 branch.
> ---
> Benchmarks showing the impact of this patch in blk performance can be
> found at:
>
> http://xenbits.xensource.com/people/royger/persistent_grants/
> ---
> drivers/block/xen-blkback/blkback.c | 292 ++++++++++++++++++++++++++++++++---
> drivers/block/xen-blkback/common.h | 17 ++
> drivers/block/xen-blkback/xenbus.c | 23 +++-
> drivers/block/xen-blkfront.c | 197 ++++++++++++++++++++----
> 4 files changed, 474 insertions(+), 55 deletions(-)
>
> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
> index 280a138..663d42d 100644
> --- a/drivers/block/xen-blkback/blkback.c
> +++ b/drivers/block/xen-blkback/blkback.c
> @@ -39,6 +39,7 @@
> #include <linux/list.h>
> #include <linux/delay.h>
> #include <linux/freezer.h>
> +#include <linux/bitmap.h>
>
> #include <xen/events.h>
> #include <xen/page.h>
> @@ -79,6 +80,7 @@ struct pending_req {
> unsigned short operation;
> int status;
> struct list_head free_list;
> + DECLARE_BITMAP(unmap_seg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
> };
>
> #define BLKBACK_INVALID_HANDLE (~0)
> @@ -99,6 +101,36 @@ struct xen_blkbk {
> static struct xen_blkbk *blkbk;
>
> /*
> + * Maximum number of grant pages that can be mapped in blkback.
> + * BLKIF_MAX_SEGMENTS_PER_REQUEST * RING_SIZE is the maximum number of
> + * pages that blkback will persistently map.
> + * Currently, this is:
> + * RING_SIZE = 32 (for all known ring types)
> + * BLKIF_MAX_SEGMENTS_PER_REQUEST = 11
> + * sizeof(struct persistent_gnt) = 48
> + * So the maximum memory used to store the grants is:
> + * 32 * 11 * 48 = 16896 bytes
> + */
> +static inline unsigned int max_mapped_grant_pages(enum blkif_protocol protocol)
> +{
> + switch (protocol) {
> + case BLKIF_PROTOCOL_NATIVE:
> + return __CONST_RING_SIZE(blkif, PAGE_SIZE) *
> + BLKIF_MAX_SEGMENTS_PER_REQUEST;
> + case BLKIF_PROTOCOL_X86_32:
> + return __CONST_RING_SIZE(blkif_x86_32, PAGE_SIZE) *
> + BLKIF_MAX_SEGMENTS_PER_REQUEST;
> + case BLKIF_PROTOCOL_X86_64:
> + return __CONST_RING_SIZE(blkif_x86_64, PAGE_SIZE) *
> + BLKIF_MAX_SEGMENTS_PER_REQUEST;
> + default:
> + BUG();
> + }
> + return 0;
> +}
> +
> +
> +/*
> * Little helpful macro to figure out the index and virtual address of the
> * pending_pages[..]. For each 'pending_req' we have have up to
> * BLKIF_MAX_SEGMENTS_PER_REQUEST (11) pages. The seg would be from 0 through
> @@ -129,6 +161,57 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
> static void make_response(struct xen_blkif *blkif, u64 id,
> unsigned short op, int st);
>
> +#define foreach_grant(pos, rbtree, node) \
> + for ((pos) = container_of(rb_first((rbtree)), typeof(*(pos)), node); \
> + &(pos)->node != NULL; \
> + (pos) = container_of(rb_next(&(pos)->node), typeof(*(pos)), node))
> +
> +
> +static void add_persistent_gnt(struct rb_root *root,
> + struct persistent_gnt *persistent_gnt)
> +{
> + struct rb_node **new = &(root->rb_node), *parent = NULL;
> + struct persistent_gnt *this;
> +
> + /* Figure out where to put new node */
> + while (*new) {
> + this = container_of(*new, struct persistent_gnt, node);
> +
> + parent = *new;
> + if (persistent_gnt->gnt < this->gnt)
> + new = &((*new)->rb_left);
> + else if (persistent_gnt->gnt > this->gnt)
> + new = &((*new)->rb_right);
> + else {
> + pr_alert(DRV_PFX " trying to add a gref that's already in the tree\n");
> + BUG();
> + }
> + }
> +
> + /* Add new node and rebalance tree. */
> + rb_link_node(&(persistent_gnt->node), parent, new);
> + rb_insert_color(&(persistent_gnt->node), root);
> +}
> +
> +static struct persistent_gnt *get_persistent_gnt(struct rb_root *root,
> + grant_ref_t gref)
> +{
> + struct persistent_gnt *data;
> + struct rb_node *node = root->rb_node;
> +
> + while (node) {
> + data = container_of(node, struct persistent_gnt, node);
> +
> + if (gref < data->gnt)
> + node = node->rb_left;
> + else if (gref > data->gnt)
> + node = node->rb_right;
> + else
> + return data;
> + }
> + return NULL;
> +}
> +
> /*
> * Retrieve from the 'pending_reqs' a free pending_req structure to be used.
> */
> @@ -275,6 +358,11 @@ int xen_blkif_schedule(void *arg)
> {
> struct xen_blkif *blkif = arg;
> struct xen_vbd *vbd = &blkif->vbd;
> + struct gnttab_unmap_grant_ref unmap[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> + struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> + struct persistent_gnt *persistent_gnt;
> + int ret = 0;
> + int segs_to_unmap = 0;
>
> xen_blkif_get(blkif);
>
> @@ -302,6 +390,36 @@ int xen_blkif_schedule(void *arg)
> print_stats(blkif);
> }
>
> + /* Free all persistent grant pages */
> + if (!RB_EMPTY_ROOT(&blkif->persistent_gnts)) {
> + foreach_grant(persistent_gnt, &blkif->persistent_gnts, node) {
> + BUG_ON(persistent_gnt->handle ==
> + BLKBACK_INVALID_HANDLE);
> + gnttab_set_unmap_op(&unmap[segs_to_unmap],
> + (unsigned long) pfn_to_kaddr(page_to_pfn(
> + persistent_gnt->page)),
> + GNTMAP_host_map,
> + persistent_gnt->handle);
> +
> + pages[segs_to_unmap] = persistent_gnt->page;
> + rb_erase(&persistent_gnt->node,
> + &blkif->persistent_gnts);
> + kfree(persistent_gnt);
> + blkif->persistent_gnt_c--;
> +
> + if (++segs_to_unmap == BLKIF_MAX_SEGMENTS_PER_REQUEST ||
> + !rb_next(&persistent_gnt->node)) {
> + ret = gnttab_unmap_refs(unmap, NULL, pages,
> + segs_to_unmap);
> + BUG_ON(ret);
> + segs_to_unmap = 0;
> + }
> + }
> + }
> +
> + BUG_ON(blkif->persistent_gnt_c != 0);
> + BUG_ON(!RB_EMPTY_ROOT(&blkif->persistent_gnts));
> +
> if (log_stats)
> print_stats(blkif);
>
> @@ -328,6 +446,8 @@ static void xen_blkbk_unmap(struct pending_req *req)
> int ret;
>
> for (i = 0; i < req->nr_pages; i++) {
> + if (!test_bit(i, req->unmap_seg))
> + continue;
> handle = pending_handle(req, i);
> if (handle == BLKBACK_INVALID_HANDLE)
> continue;
> @@ -344,12 +464,26 @@ static void xen_blkbk_unmap(struct pending_req *req)
>
> static int xen_blkbk_map(struct blkif_request *req,
> struct pending_req *pending_req,
> - struct seg_buf seg[])
> + struct seg_buf seg[],
> + struct page *pages[])
> {
> struct gnttab_map_grant_ref map[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> - int i;
> + struct persistent_gnt *persistent_gnts[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> + struct page *pages_to_gnt[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> + struct persistent_gnt *persistent_gnt = NULL;
> + struct xen_blkif *blkif = pending_req->blkif;
> + phys_addr_t addr = 0;
> + int i, j;
> + bool new_map;
> int nseg = req->u.rw.nr_segments;
> + int segs_to_map = 0;
> int ret = 0;
> + int use_persistent_gnts;
> +
> + use_persistent_gnts = (blkif->vbd.feature_gnt_persistent);
> +
> + BUG_ON(blkif->persistent_gnt_c >
> + max_mapped_grant_pages(pending_req->blkif->blk_protocol));
>
> /*
> * Fill out preq.nr_sects with proper amount of sectors, and setup
> @@ -359,36 +493,143 @@ static int xen_blkbk_map(struct blkif_request *req,
> for (i = 0; i < nseg; i++) {
> uint32_t flags;
>
> - flags = GNTMAP_host_map;
> - if (pending_req->operation != BLKIF_OP_READ)
> - flags |= GNTMAP_readonly;
> - gnttab_set_map_op(&map[i], vaddr(pending_req, i), flags,
> - req->u.rw.seg[i].gref,
> - pending_req->blkif->domid);
> + if (use_persistent_gnts)
> + persistent_gnt = get_persistent_gnt(
> + &blkif->persistent_gnts,
> + req->u.rw.seg[i].gref);
> +
> + if (persistent_gnt) {
> + /*
> + * We are using persistent grants and
> + * the grant is already mapped
> + */
> + new_map = 0;
> + } else if (use_persistent_gnts &&
> + blkif->persistent_gnt_c <
> + max_mapped_grant_pages(blkif->blk_protocol)) {
> + /*
> + * We are using persistent grants, the grant is
> + * not mapped but we have room for it
> + */
> + new_map = 1;
> + persistent_gnt = kzalloc(
> + sizeof(struct persistent_gnt),
> + GFP_KERNEL);
> + if (!persistent_gnt)
> + return -ENOMEM;
> + persistent_gnt->page = alloc_page(GFP_KERNEL);
> + if (!persistent_gnt->page) {
> + kfree(persistent_gnt);
> + return -ENOMEM;
> + }
> + persistent_gnt->gnt = req->u.rw.seg[i].gref;
> +
> + pages_to_gnt[segs_to_map] =
> + persistent_gnt->page;
> + addr = (unsigned long) pfn_to_kaddr(
> + page_to_pfn(persistent_gnt->page));
> +
> + add_persistent_gnt(&blkif->persistent_gnts,
> + persistent_gnt);
> + blkif->persistent_gnt_c++;
> + pr_debug(DRV_PFX " grant %u added to the tree of persistent grants, using %u/%u\n",
> + persistent_gnt->gnt, blkif->persistent_gnt_c,
> + max_mapped_grant_pages(blkif->blk_protocol));
> + } else {
> + /*
> + * We are either using persistent grants and
> + * hit the maximum limit of grants mapped,
> + * or we are not using persistent grants.
> + */
> + if (use_persistent_gnts &&
> + !blkif->vbd.overflow_max_grants) {
> + blkif->vbd.overflow_max_grants = 1;
> + pr_alert(DRV_PFX " domain %u, device %#x is using maximum number of persistent grants\n",
> + blkif->domid, blkif->vbd.handle);
> + }
> + new_map = 1;
> + pages[i] = blkbk->pending_page(pending_req, i);
> + addr = vaddr(pending_req, i);
> + pages_to_gnt[segs_to_map] =
> + blkbk->pending_page(pending_req, i);
> + }
> +
> + if (persistent_gnt) {
> + pages[i] = persistent_gnt->page;
> + persistent_gnts[i] = persistent_gnt;
> + } else {
> + persistent_gnts[i] = NULL;
> + }
> +
> + if (new_map) {
> + flags = GNTMAP_host_map;
> + if (!persistent_gnt &&
> + (pending_req->operation != BLKIF_OP_READ))
> + flags |= GNTMAP_readonly;
> + gnttab_set_map_op(&map[segs_to_map++], addr,
> + flags, req->u.rw.seg[i].gref,
> + blkif->domid);
> + }
> }
>
> - ret = gnttab_map_refs(map, NULL, &blkbk->pending_page(pending_req, 0), nseg);
> - BUG_ON(ret);
> + if (segs_to_map) {
> + ret = gnttab_map_refs(map, NULL, pages_to_gnt, segs_to_map);
> + BUG_ON(ret);
> + }
>
> /*
> * Now swizzle the MFN in our domain with the MFN from the other domain
> * so that when we access vaddr(pending_req,i) it has the contents of
> * the page from the other domain.
> */
> - for (i = 0; i < nseg; i++) {
> - if (unlikely(map[i].status != 0)) {
> - pr_debug(DRV_PFX "invalid buffer -- could not remap it\n");
> - map[i].handle = BLKBACK_INVALID_HANDLE;
> - ret |= 1;
> + bitmap_zero(pending_req->unmap_seg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
> + for (i = 0, j = 0; i < nseg; i++) {
> + if (!persistent_gnts[i] || !persistent_gnts[i]->handle) {
> + /* This is a newly mapped grant */
> + BUG_ON(j >= segs_to_map);
> + if (unlikely(map[j].status != 0)) {
> + pr_debug(DRV_PFX "invalid buffer -- could not remap it\n");
> + map[j].handle = BLKBACK_INVALID_HANDLE;
> + ret |= 1;
> + if (persistent_gnts[i]) {
> + rb_erase(&persistent_gnts[i]->node,
> + &blkif->persistent_gnts);
> + blkif->persistent_gnt_c--;
> + kfree(persistent_gnts[i]);
> + persistent_gnts[i] = NULL;
> + }
> + }
> + }
> + if (persistent_gnts[i]) {
> + if (!persistent_gnts[i]->handle) {
> + /*
> + * If this is a new persistent grant
> + * save the handler
> + */
> + persistent_gnts[i]->handle = map[j].handle;
> + persistent_gnts[i]->dev_bus_addr =
> + map[j++].dev_bus_addr;
> + }
> + pending_handle(pending_req, i) =
> + persistent_gnts[i]->handle;
> +
> + if (ret)
> + continue;
> +
> + seg[i].buf = persistent_gnts[i]->dev_bus_addr |
> + (req->u.rw.seg[i].first_sect << 9);
> + } else {
> + pending_handle(pending_req, i) = map[j].handle;
> + bitmap_set(pending_req->unmap_seg, i, 1);
> +
> + if (ret) {
> + j++;
> + continue;
> + }
> +
> + seg[i].buf = map[j++].dev_bus_addr |
> + (req->u.rw.seg[i].first_sect << 9);
> }
> -
> - pending_handle(pending_req, i) = map[i].handle;
> -
> - if (ret)
> - continue;
> -
> - seg[i].buf = map[i].dev_bus_addr |
> - (req->u.rw.seg[i].first_sect << 9);
> }
> return ret;
> }
> @@ -591,6 +832,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
> int operation;
> struct blk_plug plug;
> bool drain = false;
> + struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
>
> switch (req->operation) {
> case BLKIF_OP_READ:
> @@ -677,7 +919,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
> * the hypercall to unmap the grants - that is all done in
> * xen_blkbk_unmap.
> */
> - if (xen_blkbk_map(req, pending_req, seg))
> + if (xen_blkbk_map(req, pending_req, seg, pages))
> goto fail_flush;
>
> /*
> @@ -689,7 +931,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
> for (i = 0; i < nseg; i++) {
> while ((bio == NULL) ||
> (bio_add_page(bio,
> - blkbk->pending_page(pending_req, i),
> + pages[i],
> seg[i].nsec << 9,
> seg[i].buf & ~PAGE_MASK) == 0)) {
>
> diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
> index 9ad3b5e..ae7951f 100644
> --- a/drivers/block/xen-blkback/common.h
> +++ b/drivers/block/xen-blkback/common.h
> @@ -34,6 +34,7 @@
> #include <linux/vmalloc.h>
> #include <linux/wait.h>
> #include <linux/io.h>
> +#include <linux/rbtree.h>
> #include <asm/setup.h>
> #include <asm/pgalloc.h>
> #include <asm/hypervisor.h>
> @@ -160,10 +161,22 @@ struct xen_vbd {
> sector_t size;
> bool flush_support;
> bool discard_secure;
> +
> + unsigned int feature_gnt_persistent:1;
> + unsigned int overflow_max_grants:1;
> };
>
> struct backend_info;
>
> +
> +struct persistent_gnt {
> + struct page *page;
> + grant_ref_t gnt;
> + grant_handle_t handle;
> + uint64_t dev_bus_addr;
> + struct rb_node node;
> +};
> +
> struct xen_blkif {
> /* Unique identifier for this interface. */
> domid_t domid;
> @@ -190,6 +203,10 @@ struct xen_blkif {
> struct task_struct *xenblkd;
> unsigned int waiting_reqs;
>
> + /* tree to store persistent grants */
> + struct rb_root persistent_gnts;
> + unsigned int persistent_gnt_c;
> +
> /* statistics */
> unsigned long st_print;
> int st_rd_req;
> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> index 4f66171..b225026 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -118,6 +118,7 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
> atomic_set(&blkif->drain, 0);
> blkif->st_print = jiffies;
> init_waitqueue_head(&blkif->waiting_to_free);
> + blkif->persistent_gnts.rb_node = NULL;
>
> return blkif;
> }
> @@ -673,6 +674,13 @@ again:
>
> xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support);
>
> + err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u", 1);
> + if (err) {
> + xenbus_dev_fatal(dev, err, "writing %s/feature-persistent",
> + dev->nodename);
> + goto abort;
> + }
> +
> err = xenbus_printf(xbt, dev->nodename, "sectors", "%llu",
> (unsigned long long)vbd_sz(&be->blkif->vbd));
> if (err) {
> @@ -721,6 +729,7 @@ static int connect_ring(struct backend_info *be)
> struct xenbus_device *dev = be->dev;
> unsigned long ring_ref;
> unsigned int evtchn;
> + unsigned int pers_grants;
> char protocol[64] = "";
> int err;
>
> @@ -750,8 +759,18 @@ static int connect_ring(struct backend_info *be)
> xenbus_dev_fatal(dev, err, "unknown fe protocol %s", protocol);
> return -1;
> }
> - pr_info(DRV_PFX "ring-ref %ld, event-channel %d, protocol %d (%s)\n",
> - ring_ref, evtchn, be->blkif->blk_protocol, protocol);
> + err = xenbus_gather(XBT_NIL, dev->otherend,
> + "feature-persistent-grants", "%u",
> + &pers_grants, NULL);
> + if (err)
> + pers_grants = 0;
> +
> + be->blkif->vbd.feature_gnt_persistent = pers_grants;
> + be->blkif->vbd.overflow_max_grants = 0;
> +
> + pr_info(DRV_PFX "ring-ref %ld, event-channel %d, protocol %d (%s) %s\n",
> + ring_ref, evtchn, be->blkif->blk_protocol, protocol,
> + pers_grants ? "persistent grants" : "");
>
> /* Map the shared frame, irq etc. */
> err = xen_blkif_map(be->blkif, ring_ref, evtchn);
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 007db89..911d733 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -44,6 +44,7 @@
> #include <linux/mutex.h>
> #include <linux/scatterlist.h>
> #include <linux/bitmap.h>
> +#include <linux/llist.h>
>
> #include <xen/xen.h>
> #include <xen/xenbus.h>
> @@ -64,10 +65,17 @@ enum blkif_state {
> BLKIF_STATE_SUSPENDED,
> };
>
> +struct grant {
> + grant_ref_t gref;
> + unsigned long pfn;
> + struct llist_node node;
> +};
> +
> struct blk_shadow {
> struct blkif_request req;
> struct request *request;
> unsigned long frame[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> + struct grant *grants_used[BLKIF_MAX_SEGMENTS_PER_REQUEST];
> };
>
> static DEFINE_MUTEX(blkfront_mutex);
> @@ -97,6 +105,8 @@ struct blkfront_info
> struct work_struct work;
> struct gnttab_free_callback callback;
> struct blk_shadow shadow[BLK_RING_SIZE];
> + struct llist_head persistent_gnts;
> + unsigned int persistent_gnts_c;
> unsigned long shadow_free;
> unsigned int feature_flush;
> unsigned int flush_op;
> @@ -104,6 +114,7 @@ struct blkfront_info
> unsigned int feature_secdiscard:1;
> unsigned int discard_granularity;
> unsigned int discard_alignment;
> + unsigned int feature_persistent:1;
> int is_ready;
> };
>
> @@ -287,21 +298,36 @@ static int blkif_queue_request(struct request *req)
> unsigned long id;
> unsigned int fsect, lsect;
> int i, ref;
> +
> + /*
> + * Used to store if we are able to queue the request by just using
> + * existing persistent grants, or if we have to get new grants,
> + * as there are not sufficiently many free.
> + */
> + bool new_persistent_gnts;
> grant_ref_t gref_head;
> + struct page *granted_page;
> + struct grant *gnt_list_entry = NULL;
> struct scatterlist *sg;
>
> if (unlikely(info->connected != BLKIF_STATE_CONNECTED))
> return 1;
>
> - if (gnttab_alloc_grant_references(
> - BLKIF_MAX_SEGMENTS_PER_REQUEST, &gref_head) < 0) {
> - gnttab_request_free_callback(
> - &info->callback,
> - blkif_restart_queue_callback,
> - info,
> - BLKIF_MAX_SEGMENTS_PER_REQUEST);
> - return 1;
> - }
> + /* Check if we have enought grants to allocate a requests */
> + if (info->persistent_gnts_c < BLKIF_MAX_SEGMENTS_PER_REQUEST) {
> + new_persistent_gnts = 1;
> + if (gnttab_alloc_grant_references(
> + BLKIF_MAX_SEGMENTS_PER_REQUEST - info->persistent_gnts_c,
> + &gref_head) < 0) {
> + gnttab_request_free_callback(
> + &info->callback,
> + blkif_restart_queue_callback,
> + info,
> + BLKIF_MAX_SEGMENTS_PER_REQUEST);
> + return 1;
> + }
> + } else
> + new_persistent_gnts = 0;
>
> /* Fill out a communications ring structure. */
> ring_req = RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt);
> @@ -341,18 +367,73 @@ static int blkif_queue_request(struct request *req)
> BLKIF_MAX_SEGMENTS_PER_REQUEST);
>
> for_each_sg(info->sg, sg, ring_req->u.rw.nr_segments, i) {
> - buffer_mfn = pfn_to_mfn(page_to_pfn(sg_page(sg)));
> fsect = sg->offset >> 9;
> lsect = fsect + (sg->length >> 9) - 1;
> - /* install a grant reference. */
> - ref = gnttab_claim_grant_reference(&gref_head);
> - BUG_ON(ref == -ENOSPC);
>
> - gnttab_grant_foreign_access_ref(
> - ref,
> + if (info->persistent_gnts_c) {
> + BUG_ON(llist_empty(&info->persistent_gnts));
> + gnt_list_entry = llist_entry(
> + llist_del_first(&info->persistent_gnts),
> + struct grant, node);
> +
> + ref = gnt_list_entry->gref;
> + buffer_mfn = pfn_to_mfn(gnt_list_entry->pfn);
> + info->persistent_gnts_c--;
> + } else {
> + ref = gnttab_claim_grant_reference(&gref_head);
> + BUG_ON(ref == -ENOSPC);
> +
> + gnt_list_entry =
> + kmalloc(sizeof(struct grant),
> + GFP_ATOMIC);
> + if (!gnt_list_entry)
> + return -ENOMEM;
> +
> + granted_page = alloc_page(GFP_ATOMIC);
> + if (!granted_page) {
> + kfree(gnt_list_entry);
> + return -ENOMEM;
> + }
> +
> + gnt_list_entry->pfn =
> + page_to_pfn(granted_page);
> + gnt_list_entry->gref = ref;
> +
> + buffer_mfn = pfn_to_mfn(page_to_pfn(
> + granted_page));
> + gnttab_grant_foreign_access_ref(ref,
> info->xbdev->otherend_id,
> - buffer_mfn,
> - rq_data_dir(req));
> + buffer_mfn, 0);
> + }
> +
> + info->shadow[id].grants_used[i] = gnt_list_entry;
> +
> + if (rq_data_dir(req)) {
> + char *bvec_data;
> + void *shared_data;
> +
> + BUG_ON(sg->offset + sg->length > PAGE_SIZE);
> +
> + shared_data = kmap_atomic(
> + pfn_to_page(gnt_list_entry->pfn));
> + bvec_data = kmap_atomic(sg_page(sg));
> +
> + /*
> + * this does not wipe data stored outside the
> + * range sg->offset..sg->offset+sg->length.
> + * Therefore, blkback *could* see data from
> + * previous requests. This is OK as long as
> + * persistent grants are shared with just one
> + * domain. It may need refactoring if this
> + * changes
> + */
> + memcpy(shared_data + sg->offset,
> + bvec_data + sg->offset,
> + sg->length);
> +
> + kunmap_atomic(bvec_data);
> + kunmap_atomic(shared_data);
> + }
>
> info->shadow[id].frame[i] = mfn_to_pfn(buffer_mfn);
> ring_req->u.rw.seg[i] =
> @@ -368,7 +449,8 @@ static int blkif_queue_request(struct request *req)
> /* Keep a private copy so we can reissue requests when recovering. */
> info->shadow[id].req = *ring_req;
>
> - gnttab_free_grant_references(gref_head);
> + if (new_persistent_gnts)
> + gnttab_free_grant_references(gref_head);
>
> return 0;
> }
> @@ -480,12 +562,13 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size)
> static void xlvbd_flush(struct blkfront_info *info)
> {
> blk_queue_flush(info->rq, info->feature_flush);
> - printk(KERN_INFO "blkfront: %s: %s: %s\n",
> + printk(KERN_INFO "blkfront: %s: %s: %s %s\n",
> info->gd->disk_name,
> info->flush_op == BLKIF_OP_WRITE_BARRIER ?
> "barrier" : (info->flush_op == BLKIF_OP_FLUSH_DISKCACHE ?
> "flush diskcache" : "barrier or flush"),
> - info->feature_flush ? "enabled" : "disabled");
> + info->feature_flush ? "enabled" : "disabled",
> + info->feature_persistent ? "using persistent grants" : "");
> }
>
> static int xen_translate_vdev(int vdevice, int *minor, unsigned int *offset)
> @@ -707,6 +790,9 @@ static void blkif_restart_queue(struct work_struct *work)
>
> static void blkif_free(struct blkfront_info *info, int suspend)
> {
> + struct llist_node *all_gnts;
> + struct grant *persistent_gnt;
> +
> /* Prevent new requests being issued until we fix things up. */
> spin_lock_irq(&info->io_lock);
> info->connected = suspend ?
> @@ -714,6 +800,17 @@ static void blkif_free(struct blkfront_info *info, int suspend)
> /* No more blkif_request(). */
> if (info->rq)
> blk_stop_queue(info->rq);
> +
> + /* Remove all persistent grants */
> + if (info->persistent_gnts_c) {
> + all_gnts = llist_del_all(&info->persistent_gnts);
> + llist_for_each_entry(persistent_gnt, all_gnts, node) {
> + gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
> + kfree(persistent_gnt);
> + }
> + info->persistent_gnts_c = 0;
> + }
> +
> /* No more gnttab callback work. */
> gnttab_cancel_free_callback(&info->callback);
> spin_unlock_irq(&info->io_lock);
> @@ -734,13 +831,42 @@ static void blkif_free(struct blkfront_info *info, int suspend)
>
> }
>
> -static void blkif_completion(struct blk_shadow *s)
> +static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
> + struct blkif_response *bret)
> {
> int i;
> - /* Do not let BLKIF_OP_DISCARD as nr_segment is in the same place
> - * flag. */
> - for (i = 0; i < s->req.u.rw.nr_segments; i++)
> - gnttab_end_foreign_access(s->req.u.rw.seg[i].gref, 0, 0UL);
> + struct bio_vec *bvec;
> + struct req_iterator iter;
> + unsigned long flags;
> + char *bvec_data;
> + void *shared_data;
> + unsigned int offset = 0;
> +
> + if (bret->operation == BLKIF_OP_READ) {
> + /*
> + * Copy the data received from the backend into the bvec.
> + * Since bv_offset can be different than 0, and bv_len different
> + * than PAGE_SIZE, we have to keep track of the current offset,
> + * to be sure we are copying the data from the right shared page.
> + */
> + rq_for_each_segment(bvec, s->request, iter) {
> + BUG_ON((bvec->bv_offset + bvec->bv_len) > PAGE_SIZE);
> + i = offset >> PAGE_SHIFT;
> + shared_data = kmap_atomic(
> + pfn_to_page(s->grants_used[i]->pfn));
> + bvec_data = bvec_kmap_irq(bvec, &flags);
> + memcpy(bvec_data, shared_data + bvec->bv_offset,
> + bvec->bv_len);
> + bvec_kunmap_irq(bvec_data, &flags);
> + kunmap_atomic(shared_data);
> + offset += bvec->bv_len;
> + }
> + }
> + /* Add the persistent grant into the list of free grants */
> + for (i = 0; i < s->req.u.rw.nr_segments; i++) {
> + llist_add(&s->grants_used[i]->node, &info->persistent_gnts);
> + info->persistent_gnts_c++;
> + }
> }
>
> static irqreturn_t blkif_interrupt(int irq, void *dev_id)
> @@ -783,7 +909,7 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
> req = info->shadow[id].request;
>
> if (bret->operation != BLKIF_OP_DISCARD)
> - blkif_completion(&info->shadow[id]);
> + blkif_completion(&info->shadow[id], info, bret);
>
> if (add_id_to_freelist(info, id)) {
> WARN(1, "%s: response to %s (id %ld) couldn't be recycled!\n",
> @@ -942,6 +1068,11 @@ again:
> message = "writing protocol";
> goto abort_transaction;
> }
> + err = xenbus_printf(xbt, dev->nodename,
> + "feature-persistent-grants", "%u", 1);
> + if (err)
> + dev_warn(&dev->dev,
> + "writing persistent grants feature to xenbus");
>
> err = xenbus_transaction_end(xbt, 0);
> if (err) {
> @@ -1029,6 +1160,8 @@ static int blkfront_probe(struct xenbus_device *dev,
> spin_lock_init(&info->io_lock);
> info->xbdev = dev;
> info->vdevice = vdevice;
> + init_llist_head(&info->persistent_gnts);
> + info->persistent_gnts_c = 0;
> info->connected = BLKIF_STATE_DISCONNECTED;
> INIT_WORK(&info->work, blkif_restart_queue);
>
> @@ -1093,7 +1226,7 @@ static int blkif_recover(struct blkfront_info *info)
> req->u.rw.seg[j].gref,
> info->xbdev->otherend_id,
> pfn_to_mfn(info->shadow[req->u.rw.id].frame[j]),
> - rq_data_dir(info->shadow[req->u.rw.id].request));
> + 0);
> }
> info->shadow[req->u.rw.id].req = *req;
>
> @@ -1225,7 +1358,7 @@ static void blkfront_connect(struct blkfront_info *info)
> unsigned long sector_size;
> unsigned int binfo;
> int err;
> - int barrier, flush, discard;
> + int barrier, flush, discard, persistent;
>
> switch (info->connected) {
> case BLKIF_STATE_CONNECTED:
> @@ -1303,6 +1436,14 @@ static void blkfront_connect(struct blkfront_info *info)
> if (!err && discard)
> blkfront_setup_discard(info);
>
> + err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
> + "feature-persistent", "%u", &persistent,
> + NULL);
> + if (err)
> + info->feature_persistent = 0;
> + else
> + info->feature_persistent = persistent;
> +
> err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size);
> if (err) {
> xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",
> --
> 1.7.7.5 (Apple Git-26)
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