[PATCH 3/6] nfs: Eliminate nfs_get_user_pages()

From: Chuck Lever
Date: Fri May 19 2006 - 14:01:07 EST

Neil Brown observed that the kmalloc() in nfs_get_user_pages() is more
likely to fail if the I/O is large enough to require the allocation of more
than a single page to keep track of all the pinned pages in the user's
buffer.

Instead of tracking one large page array per dreq/iocb, track pages per
nfs_read/write_data, just like the cached I/O path does. An array for
pages is already allocated for us by nfs_readdata_alloc() (and the write
and commit equivalents).

This is also required for adding support for vectored I/O to the NFS direct
I/O path.

The original reason to pin the user buffer and allocate all the NFS data
structures before trying to schedule I/O was to ensure all needed resources
are allocated on the client before starting to send requests. This reduces
the chance that resource exhaustion on the client will cause a short read
or write.

On the other hand, for an application making very large application I/O
requests, this means that it will be nearly impossible for the application
to make forward progress on a resource-limited client.

Thus, moving the buffer pinning functionality into the I/O scheduling
loops should be good for scalability. The next patch will do the same for
NFS data structure allocation.

Signed-off-by: Chuck Lever <cel@xxxxxxxxxx>
---

fs/nfs/direct.c | 173 ++++++++++++++++++++++++-----------------------
include/linux/nfs_xdr.h | 2 +
2 files changed, 91 insertions(+), 84 deletions(-)

diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index aef0b98..ae451db 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -73,8 +73,6 @@ struct nfs_direct_req {
struct nfs_open_context *ctx; /* file open context info */
struct kiocb * iocb; /* controlling i/o request */
struct inode * inode; /* target file of i/o */
- struct page ** pages; /* pages in our buffer */
- unsigned int npages; /* count of pages */

/* completion state */
spinlock_t lock; /* protect completion state */
@@ -105,6 +103,16 @@ static inline int nfs_direct_dec_outstan
return (result == 0);
}

+static inline unsigned long nfs_count_pages(unsigned long user_addr, size_t size)
+{
+ unsigned long page_count;
+
+ page_count = (user_addr + size + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ page_count -= user_addr >> PAGE_SHIFT;
+
+ return page_count;
+}
+
/**
* nfs_direct_IO - NFS address space operation for direct I/O
* @rw: direction (read or write)
@@ -127,50 +135,21 @@ ssize_t nfs_direct_IO(int rw, struct kio
return -EINVAL;
}

-static void nfs_free_user_pages(struct page **pages, int npages, int do_dirty)
+static void nfs_dirty_user_pages(struct page **pages, int npages)
{
int i;
for (i = 0; i < npages; i++) {
struct page *page = pages[i];
- if (do_dirty && !PageCompound(page))
+ if (!PageCompound(page))
set_page_dirty_lock(page);
- page_cache_release(page);
}
- kfree(pages);
}

-static inline int nfs_get_user_pages(int rw, unsigned long user_addr, size_t size, struct page ***pages)
+static void nfs_release_user_pages(struct page **pages, int npages)
{
- int result = -ENOMEM;
- unsigned long page_count;
- size_t array_size;
-
- page_count = (user_addr + size + PAGE_SIZE - 1) >> PAGE_SHIFT;
- page_count -= user_addr >> PAGE_SHIFT;
-
- array_size = (page_count * sizeof(struct page *));
- *pages = kmalloc(array_size, GFP_KERNEL);
- if (*pages) {
- down_read(&current->mm->mmap_sem);
- result = get_user_pages(current, current->mm, user_addr,
- page_count, (rw == READ), 0,
- *pages, NULL);
- up_read(&current->mm->mmap_sem);
- if (result != page_count) {
- /*
- * If we got fewer pages than expected from
- * get_user_pages(), the user buffer runs off the
- * end of a mapping; return EFAULT.
- */
- if (result >= 0) {
- nfs_free_user_pages(*pages, result, 0);
- result = -EFAULT;
- } else
- kfree(*pages);
- *pages = NULL;
- }
- }
- return result;
+ int i;
+ for (i = 0; i < npages; i++)
+ page_cache_release(pages[i]);
}

static inline struct nfs_direct_req *nfs_direct_req_alloc(void)
@@ -229,18 +208,11 @@ out:
}

/*
- * We must hold a reference to all the pages in this direct read request
- * until the RPCs complete. This could be long *after* we are woken up in
- * nfs_direct_wait (for instance, if someone hits ^C on a slow server).
- *
- * In addition, synchronous I/O uses a stack-allocated iocb. Thus we
- * can't trust the iocb is still valid here if this is a synchronous
- * request. If the waiter is woken prematurely, the iocb is long gone.
+ * Synchronous I/O uses a stack-allocated iocb. Thus we can't trust
+ * the iocb is still valid here if this is a synchronous request.
*/
static void nfs_direct_complete(struct nfs_direct_req *dreq)
{
- nfs_free_user_pages(dreq->pages, dreq->npages, 1);
-
if (dreq->iocb) {
long res = (long) dreq->error;
if (!res)
@@ -295,6 +267,11 @@ static struct nfs_direct_req *nfs_direct
return dreq;
}

+/*
+ * We must hold a reference to all the pages in this direct read request
+ * until the RPCs complete. This could be long *after* we are woken up in
+ * nfs_direct_wait (for instance, if someone hits ^C on a slow server).
+ */
static void nfs_direct_read_result(struct rpc_task *task, void *calldata)
{
struct nfs_read_data *data = calldata;
@@ -303,6 +280,9 @@ static void nfs_direct_read_result(struc
if (nfs_readpage_result(task, data) != 0)
return;

+ nfs_dirty_user_pages(data->pagevec, data->npages);
+ nfs_release_user_pages(data->pagevec, data->npages);
+
spin_lock(&dreq->lock);

if (likely(task->tk_status >= 0))
@@ -316,6 +296,7 @@ static void nfs_direct_read_result(struc
}

spin_unlock(&dreq->lock);
+
nfs_direct_complete(dreq);
}

@@ -333,14 +314,13 @@ static void nfs_direct_read_schedule(str
struct nfs_open_context *ctx = dreq->ctx;
struct inode *inode = ctx->dentry->d_inode;
struct list_head *list = &dreq->list;
- struct page **pages = dreq->pages;
size_t rsize = NFS_SERVER(inode)->rsize;
- unsigned int curpage, pgbase;
+ unsigned int pgbase;
+ unsigned long result;
+ struct nfs_read_data *data;

- curpage = 0;
pgbase = user_addr & ~PAGE_MASK;
do {
- struct nfs_read_data *data;
size_t bytes;

bytes = rsize;
@@ -351,13 +331,21 @@ static void nfs_direct_read_schedule(str
data = list_entry(list->next, struct nfs_read_data, pages);
list_del_init(&data->pages);

+ data->npages = nfs_count_pages(user_addr, bytes);
+ down_read(&current->mm->mmap_sem);
+ result = get_user_pages(current, current->mm, user_addr,
+ data->npages, 1, 0, data->pagevec, NULL);
+ up_read(&current->mm->mmap_sem);
+ if (unlikely(result < data->npages))
+ goto out_err;
+
data->inode = inode;
data->cred = ctx->cred;
data->args.fh = NFS_FH(inode);
data->args.context = ctx;
data->args.offset = pos;
data->args.pgbase = pgbase;
- data->args.pages = &pages[curpage];
+ data->args.pages = data->pagevec;
data->args.count = bytes;
data->res.fattr = &data->fattr;
data->res.eof = 0;
@@ -380,17 +368,32 @@ static void nfs_direct_read_schedule(str
bytes,
(unsigned long long)data->args.offset);

+ user_addr += bytes;
pos += bytes;
pgbase += bytes;
- curpage += pgbase >> PAGE_SHIFT;
pgbase &= ~PAGE_MASK;

count -= bytes;
} while (count != 0);
BUG_ON(!list_empty(list));
+ return;
+
+ /* If get_user_pages fails, we stop sending reads. Read length
+ * accounting is handled by nfs_direct_read_result() . */
+out_err:
+ nfs_release_user_pages(data->pagevec, result);
+
+ list_add(&data->pages, list);
+ while (!list_empty(list)) {
+ data = list_entry(list->next, struct nfs_read_data, pages);
+ list_del(&data->pages);
+ nfs_readdata_free(data);
+ if (nfs_direct_dec_outstanding(dreq))
+ nfs_direct_complete(dreq);
+ }
}

-static ssize_t nfs_direct_read(struct kiocb *iocb, unsigned long user_addr, size_t count, loff_t pos, struct page **pages, unsigned int nr_pages)
+static ssize_t nfs_direct_read(struct kiocb *iocb, unsigned long user_addr, size_t count, loff_t pos)
{
ssize_t result;
sigset_t oldset;
@@ -402,8 +405,6 @@ static ssize_t nfs_direct_read(struct ki
if (!dreq)
return -ENOMEM;

- dreq->pages = pages;
- dreq->npages = nr_pages;
dreq->inode = inode;
dreq->ctx = get_nfs_open_context((struct nfs_open_context *)iocb->ki_filp->private_data);
if (!is_sync_kiocb(iocb))
@@ -424,6 +425,7 @@ static void nfs_direct_free_writedata(st
while (!list_empty(&dreq->list)) {
struct nfs_write_data *data = list_entry(dreq->list.next, struct nfs_write_data, pages);
list_del(&data->pages);
+ nfs_release_user_pages(data->pagevec, data->npages);
nfs_writedata_release(data);
}
}
@@ -677,14 +679,13 @@ static void nfs_direct_write_schedule(st
struct nfs_open_context *ctx = dreq->ctx;
struct inode *inode = ctx->dentry->d_inode;
struct list_head *list = &dreq->list;
- struct page **pages = dreq->pages;
size_t wsize = NFS_SERVER(inode)->wsize;
- unsigned int curpage, pgbase;
+ unsigned int pgbase;
+ unsigned long result;
+ struct nfs_write_data *data;

- curpage = 0;
pgbase = user_addr & ~PAGE_MASK;
do {
- struct nfs_write_data *data;
size_t bytes;

bytes = wsize;
@@ -693,6 +694,15 @@ static void nfs_direct_write_schedule(st

BUG_ON(list_empty(list));
data = list_entry(list->next, struct nfs_write_data, pages);
+
+ data->npages = nfs_count_pages(user_addr, bytes);
+ down_read(&current->mm->mmap_sem);
+ result = get_user_pages(current, current->mm, user_addr,
+ data->npages, 0, 0, data->pagevec, NULL);
+ up_read(&current->mm->mmap_sem);
+ if (unlikely(result < data->npages))
+ goto out_err;
+
list_move_tail(&data->pages, &dreq->rewrite_list);

data->inode = inode;
@@ -701,7 +711,7 @@ static void nfs_direct_write_schedule(st
data->args.context = ctx;
data->args.offset = pos;
data->args.pgbase = pgbase;
- data->args.pages = &pages[curpage];
+ data->args.pages = data->pagevec;
data->args.count = bytes;
data->res.fattr = &data->fattr;
data->res.count = bytes;
@@ -725,17 +735,32 @@ static void nfs_direct_write_schedule(st
bytes,
(unsigned long long)data->args.offset);

+ user_addr += bytes;
pos += bytes;
pgbase += bytes;
- curpage += pgbase >> PAGE_SHIFT;
pgbase &= ~PAGE_MASK;

count -= bytes;
} while (count != 0);
BUG_ON(!list_empty(list));
+ return;
+
+ /* If get_user_pages fails, we stop sending writes. Write length
+ * accounting is handled by nfs_direct_write_result() . */
+out_err:
+ nfs_release_user_pages(data->pagevec, result);
+
+ list_add(&data->pages, list);
+ while (!list_empty(list)) {
+ data = list_entry(list->next, struct nfs_write_data, pages);
+ list_del(&data->pages);
+ nfs_writedata_free(data);
+ if (nfs_direct_dec_outstanding(dreq))
+ nfs_direct_write_complete(dreq, inode);
+ }
}

-static ssize_t nfs_direct_write(struct kiocb *iocb, unsigned long user_addr, size_t count, loff_t pos, struct page **pages, int nr_pages)
+static ssize_t nfs_direct_write(struct kiocb *iocb, unsigned long user_addr, size_t count, loff_t pos)
{
ssize_t result;
sigset_t oldset;
@@ -751,8 +776,6 @@ static ssize_t nfs_direct_write(struct k
if (dreq->commit_data == NULL || count < wsize)
sync = FLUSH_STABLE;

- dreq->pages = pages;
- dreq->npages = nr_pages;
dreq->inode = inode;
dreq->ctx = get_nfs_open_context((struct nfs_open_context *)iocb->ki_filp->private_data);
if (!is_sync_kiocb(iocb))
@@ -795,8 +818,6 @@ ssize_t nfs_file_direct_read(struct kioc
unsigned long nr_segs, loff_t pos)
{
ssize_t retval = -EINVAL;
- int page_count;
- struct page **pages;
struct file *file = iocb->ki_filp;
struct address_space *mapping = file->f_mapping;
/* XXX: temporary */
@@ -824,14 +845,7 @@ ssize_t nfs_file_direct_read(struct kioc
if (retval)
goto out;

- retval = nfs_get_user_pages(READ, (unsigned long) buf,
- count, &pages);
- if (retval < 0)
- goto out;
- page_count = retval;
-
- retval = nfs_direct_read(iocb, (unsigned long) buf, count, pos,
- pages, page_count);
+ retval = nfs_direct_read(iocb, (unsigned long) buf, count, pos);
if (retval > 0)
iocb->ki_pos = pos + retval;

@@ -868,8 +882,6 @@ ssize_t nfs_file_direct_write(struct kio
unsigned long nr_segs, loff_t pos)
{
ssize_t retval;
- int page_count;
- struct page **pages;
struct file *file = iocb->ki_filp;
struct address_space *mapping = file->f_mapping;
/* XXX: temporary */
@@ -903,14 +915,7 @@ ssize_t nfs_file_direct_write(struct kio
if (retval)
goto out;

- retval = nfs_get_user_pages(WRITE, (unsigned long) buf,
- count, &pages);
- if (retval < 0)
- goto out;
- page_count = retval;
-
- retval = nfs_direct_write(iocb, (unsigned long) buf, count,
- pos, pages, page_count);
+ retval = nfs_direct_write(iocb, (unsigned long) buf, count, pos);

/*
* XXX: nfs_end_data_update() already ensures this file's
diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index 7c7320f..102b5c8 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -729,6 +729,7 @@ struct nfs_read_data {
struct list_head pages; /* Coalesced read requests */
struct nfs_page *req; /* multi ops per nfs_page */
struct page **pagevec;
+ int npages; /* active pages in pagevec */
struct nfs_readargs args;
struct nfs_readres res;
#ifdef CONFIG_NFS_V4
@@ -747,6 +748,7 @@ struct nfs_write_data {
struct list_head pages; /* Coalesced requests we wish to flush */
struct nfs_page *req; /* multi ops per nfs_page */
struct page **pagevec;
+ int npages; /* active pages in pagevec */
struct nfs_writeargs args; /* argument struct */
struct nfs_writeres res; /* result struct */
#ifdef CONFIG_NFS_V4
-
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