[PATCH v6 5/9] hugetlb: disable region_add file_region coalescing

From: Mina Almasry
Date: Sat Oct 12 2019 - 20:31:09 EST

A follow up patch in this series adds hugetlb cgroup uncharge info the
file_region entries in resv->regions. The cgroup uncharge info may
differ for different regions, so they can no longer be coalesced at
region_add time. So, disable region coalescing in region_add in this
patch.

Behavior change:

Say a resv_map exists like this [0->1], [2->3], and [5->6].

Then a region_chg/add call comes in region_chg/add(f=0, t=5).

Old code would generate resv->regions: [0->5], [5->6].
New code would generate resv->regions: [0->1], [1->2], [2->3], [3->5],
[5->6].

Special care needs to be taken to handle the resv->adds_in_progress
variable correctly. In the past, only 1 region would be added for every
region_chg and region_add call. But now, each call may add multiple
regions, so we can no longer increment adds_in_progress by 1 in region_chg,
or decrement adds_in_progress by 1 after region_add or region_abort. Instead,
region_chg calls add_reservation_in_range() to count the number of regions
needed and allocates those, and that info is passed to region_add and
region_abort to decrement adds_in_progress correctly.

Signed-off-by: Mina Almasry <almasrymina@xxxxxxxxxx>

---

Changes in v6:
- Fix bug in number of region_caches allocated by region_chg

---
mm/hugetlb.c | 256 +++++++++++++++++++++++++++++----------------------
1 file changed, 147 insertions(+), 109 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 4a60d7d44b4c3..f9c1947925bb9 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -244,6 +244,12 @@ struct file_region {
long to;
};

+/* Helper that removes a struct file_region from the resv_map cache and returns
+ * it for use.
+ */
+static struct file_region *
+get_file_region_entry_from_cache(struct resv_map *resv, long from, long to);
+
/* Must be called with resv->lock held. Calling this with count_only == true
* will count the number of pages to be added but will not modify the linked
* list.
@@ -251,51 +257,61 @@ struct file_region {
static long add_reservation_in_range(struct resv_map *resv, long f, long t,
bool count_only)
{
- long chg = 0;
+ long add = 0;
struct list_head *head = &resv->regions;
+ long last_accounted_offset = f;
struct file_region *rg = NULL, *trg = NULL, *nrg = NULL;

- /* Locate the region we are before or in. */
- list_for_each_entry (rg, head, link)
- if (f <= rg->to)
- break;
-
- /* Round our left edge to the current segment if it encloses us. */
- if (f > rg->from)
- f = rg->from;
-
- chg = t - f;
+ /* In this loop, we essentially handle an entry for the range
+ * last_accounted_offset -> rg->from, at every iteration, with some
+ * bounds checking.
+ */
+ list_for_each_entry_safe(rg, trg, head, link) {
+ /* Skip irrelevant regions that start before our range. */
+ if (rg->from < f) {
+ /* If this region ends after the last accounted offset,
+ * then we need to update last_accounted_offset.
+ */
+ if (rg->to > last_accounted_offset)
+ last_accounted_offset = rg->to;
+ continue;
+ }

- /* Check for and consume any regions we now overlap with. */
- nrg = rg;
- list_for_each_entry_safe (rg, trg, rg->link.prev, link) {
- if (&rg->link == head)
- break;
+ /* When we find a region that starts beyond our range, we've
+ * finished.
+ */
if (rg->from > t)
break;

- /* We overlap with this area, if it extends further than
- * us then we must extend ourselves. Account for its
- * existing reservation.
+ /* Add an entry for last_accounted_offset -> rg->from, and
+ * update last_accounted_offset.
*/
- if (rg->to > t) {
- chg += rg->to - t;
- t = rg->to;
+ if (rg->from > last_accounted_offset) {
+ add += rg->from - last_accounted_offset;
+ if (!count_only) {
+ nrg = get_file_region_entry_from_cache(
+ resv, last_accounted_offset, rg->from);
+ list_add(&nrg->link, rg->link.prev);
+ }
}
- chg -= rg->to - rg->from;

- if (!count_only && rg != nrg) {
- list_del(&rg->link);
- kfree(rg);
- }
+ last_accounted_offset = rg->to;
}

- if (!count_only) {
- nrg->from = f;
- nrg->to = t;
+ /* Handle the case where our range extends beyond
+ * last_accounted_offset.
+ */
+ if (last_accounted_offset < t) {
+ add += t - last_accounted_offset;
+ if (!count_only) {
+ nrg = get_file_region_entry_from_cache(
+ resv, last_accounted_offset, t);
+ list_add(&nrg->link, rg->link.prev);
+ }
+ last_accounted_offset = t;
}

- return chg;
+ return add;
}

/*
@@ -305,46 +321,24 @@ static long add_reservation_in_range(struct resv_map *resv, long f, long t,
* must exist in the cache due to the previous call to region_chg with
* the same range.
*
+ * regions_needed is the out value provided by a previous
+ * call to region_chg.
+ *
* Return the number of new huge pages added to the map. This
* number is greater than or equal to zero.
*/
-static long region_add(struct resv_map *resv, long f, long t)
+static long region_add(struct resv_map *resv, long f, long t,
+ long regions_needed)
{
- struct list_head *head = &resv->regions;
- struct file_region *rg, *nrg;
long add = 0;

spin_lock(&resv->lock);
- /* Locate the region we are either in or before. */
- list_for_each_entry(rg, head, link)
- if (f <= rg->to)
- break;
-
- /*
- * If no region exists which can be expanded to include the
- * specified range, pull a region descriptor from the cache
- * and use it for this range.
- */
- if (&rg->link == head || t < rg->from) {
- VM_BUG_ON(resv->region_cache_count <= 0);
-
- resv->region_cache_count--;
- nrg = list_first_entry(&resv->region_cache, struct file_region,
- link);
- list_del(&nrg->link);

- nrg->from = f;
- nrg->to = t;
- list_add(&nrg->link, rg->link.prev);
-
- add += t - f;
- goto out_locked;
- }
+ VM_BUG_ON(resv->region_cache_count < regions_needed);

add = add_reservation_in_range(resv, f, t, false);
+ resv->adds_in_progress -= regions_needed;

-out_locked:
- resv->adds_in_progress--;
spin_unlock(&resv->lock);
VM_BUG_ON(add < 0);
return add;
@@ -361,31 +355,39 @@ static long region_add(struct resv_map *resv, long f, long t)
* as a placeholder, so that the subsequent region_add
* call will have all the regions it needs and will not fail.
*
+ * out_regions_needed is the number of regions added to the
+ * resv->region_cache_count. This value needs to be provided to a follow up
+ * call to region_add or region_abort for proper accounting.
+ *
* Returns the number of huge pages that need to be added to the existing
* reservation map for the range [f, t). This number is greater or equal to
* zero. -ENOMEM is returned if a new file_region structure or cache entry
* is needed and can not be allocated.
*/
-static long region_chg(struct resv_map *resv, long f, long t)
+static long region_chg(struct resv_map *resv, long f, long t,
+ long *out_regions_needed)
{
+ struct file_region *trg = NULL;
long chg = 0;

+ /* Allocate the maximum number of regions we're going to need for this
+ * reservation. The maximum number of regions we're going to need is
+ * (t - f) / 2 + 1, which corresponds to a region with alternating
+ * reserved and unreserved pages.
+ */
+ *out_regions_needed = (t - f) / 2 + 1;
+
spin_lock(&resv->lock);
-retry_locked:
- resv->adds_in_progress++;
+
+ resv->adds_in_progress += *out_regions_needed;

/*
* Check for sufficient descriptors in the cache to accommodate
* the number of in progress add operations.
*/
- if (resv->adds_in_progress > resv->region_cache_count) {
- struct file_region *trg;
-
- VM_BUG_ON(resv->adds_in_progress - resv->region_cache_count > 1);
+ while (resv->region_cache_count < resv->adds_in_progress) {
/* Must drop lock to allocate a new descriptor. */
- resv->adds_in_progress--;
spin_unlock(&resv->lock);
-
trg = kmalloc(sizeof(*trg), GFP_KERNEL);
if (!trg)
return -ENOMEM;
@@ -393,9 +395,9 @@ static long region_chg(struct resv_map *resv, long f, long t)
spin_lock(&resv->lock);
list_add(&trg->link, &resv->region_cache);
resv->region_cache_count++;
- goto retry_locked;
}

+ /* Count how many hugepages in this range are NOT respresented. */
chg = add_reservation_in_range(resv, f, t, true);

spin_unlock(&resv->lock);
@@ -407,17 +409,19 @@ static long region_chg(struct resv_map *resv, long f, long t)
* of the resv_map keeps track of the operations in progress between
* calls to region_chg and region_add. Operations are sometimes
* aborted after the call to region_chg. In such cases, region_abort
- * is called to decrement the adds_in_progress counter.
+ * is called to decrement the adds_in_progress counter. regions_needed
+ * is the value returned by the region_chg call, it is used to decrement
+ * the adds_in_progress counter.
*
* NOTE: The range arguments [f, t) are not needed or used in this
* routine. They are kept to make reading the calling code easier as
* arguments will match the associated region_chg call.
*/
-static void region_abort(struct resv_map *resv, long f, long t)
+static void region_abort(struct resv_map *resv, long f, long t,
+ long regions_needed)
{
spin_lock(&resv->lock);
- VM_BUG_ON(!resv->region_cache_count);
- resv->adds_in_progress--;
+ resv->adds_in_progress -= regions_needed;
spin_unlock(&resv->lock);
}

@@ -1898,9 +1902,10 @@ enum vma_resv_mode {
VMA_END_RESV,
VMA_ADD_RESV,
};
-static long __vma_reservation_common(struct hstate *h,
- struct vm_area_struct *vma, unsigned long addr,
- enum vma_resv_mode mode)
+static long
+__vma_reservation_common(struct hstate *h, struct vm_area_struct *vma,
+ unsigned long addr, enum vma_resv_mode mode,
+ long *out_regions_needed, long in_regions_needed)
{
struct resv_map *resv;
pgoff_t idx;
@@ -1913,20 +1918,24 @@ static long __vma_reservation_common(struct hstate *h,
idx = vma_hugecache_offset(h, vma, addr);
switch (mode) {
case VMA_NEEDS_RESV:
- ret = region_chg(resv, idx, idx + 1);
+ VM_BUG_ON(!out_regions_needed);
+ ret = region_chg(resv, idx, idx + 1, out_regions_needed);
break;
case VMA_COMMIT_RESV:
- ret = region_add(resv, idx, idx + 1);
+ VM_BUG_ON(in_regions_needed == -1);
+ ret = region_add(resv, idx, idx + 1, in_regions_needed);
break;
case VMA_END_RESV:
- region_abort(resv, idx, idx + 1);
+ VM_BUG_ON(in_regions_needed == -1);
+ region_abort(resv, idx, idx + 1, in_regions_needed);
ret = 0;
break;
case VMA_ADD_RESV:
+ VM_BUG_ON(in_regions_needed == -1);
if (vma->vm_flags & VM_MAYSHARE)
- ret = region_add(resv, idx, idx + 1);
+ ret = region_add(resv, idx, idx + 1, in_regions_needed);
else {
- region_abort(resv, idx, idx + 1);
+ region_abort(resv, idx, idx + 1, in_regions_needed);
ret = region_del(resv, idx, idx + 1);
}
break;
@@ -1959,28 +1968,32 @@ static long __vma_reservation_common(struct hstate *h,
return ret < 0 ? ret : 0;
}

-static long vma_needs_reservation(struct hstate *h,
- struct vm_area_struct *vma, unsigned long addr)
+static long vma_needs_reservation(struct hstate *h, struct vm_area_struct *vma,
+ unsigned long addr, long *out_regions_needed)
{
- return __vma_reservation_common(h, vma, addr, VMA_NEEDS_RESV);
+ return __vma_reservation_common(h, vma, addr, VMA_NEEDS_RESV,
+ out_regions_needed, -1);
}

-static long vma_commit_reservation(struct hstate *h,
- struct vm_area_struct *vma, unsigned long addr)
+static long vma_commit_reservation(struct hstate *h, struct vm_area_struct *vma,
+ unsigned long addr, long regions_needed)
{
- return __vma_reservation_common(h, vma, addr, VMA_COMMIT_RESV);
+ return __vma_reservation_common(h, vma, addr, VMA_COMMIT_RESV, NULL,
+ regions_needed);
}

-static void vma_end_reservation(struct hstate *h,
- struct vm_area_struct *vma, unsigned long addr)
+static void vma_end_reservation(struct hstate *h, struct vm_area_struct *vma,
+ unsigned long addr, long regions_needed)
{
- (void)__vma_reservation_common(h, vma, addr, VMA_END_RESV);
+ (void)__vma_reservation_common(h, vma, addr, VMA_END_RESV, NULL,
+ regions_needed);
}

-static long vma_add_reservation(struct hstate *h,
- struct vm_area_struct *vma, unsigned long addr)
+static long vma_add_reservation(struct hstate *h, struct vm_area_struct *vma,
+ unsigned long addr, long regions_needed)
{
- return __vma_reservation_common(h, vma, addr, VMA_ADD_RESV);
+ return __vma_reservation_common(h, vma, addr, VMA_ADD_RESV, NULL,
+ regions_needed);
}

/*
@@ -1998,8 +2011,10 @@ static void restore_reserve_on_error(struct hstate *h,
struct vm_area_struct *vma, unsigned long address,
struct page *page)
{
+ long regions_needed = 0;
if (unlikely(PagePrivate(page))) {
- long rc = vma_needs_reservation(h, vma, address);
+ long rc =
+ vma_needs_reservation(h, vma, address, &regions_needed);

if (unlikely(rc < 0)) {
/*
@@ -2015,7 +2030,8 @@ static void restore_reserve_on_error(struct hstate *h,
*/
ClearPagePrivate(page);
} else if (rc) {
- rc = vma_add_reservation(h, vma, address);
+ rc = vma_add_reservation(h, vma, address,
+ regions_needed);
if (unlikely(rc < 0))
/*
* See above comment about rare out of
@@ -2023,7 +2039,7 @@ static void restore_reserve_on_error(struct hstate *h,
*/
ClearPagePrivate(page);
} else
- vma_end_reservation(h, vma, address);
+ vma_end_reservation(h, vma, address, regions_needed);
}
}

@@ -2037,6 +2053,7 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
long gbl_chg;
int ret, idx;
struct hugetlb_cgroup *h_cg;
+ long regions_needed = 0;

idx = hstate_index(h);
/*
@@ -2044,7 +2061,8 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
* has a reservation for the page to be allocated. A return
* code of zero indicates a reservation exists (no change).
*/
- map_chg = gbl_chg = vma_needs_reservation(h, vma, addr);
+ map_chg = gbl_chg =
+ vma_needs_reservation(h, vma, addr, &regions_needed);
if (map_chg < 0)
return ERR_PTR(-ENOMEM);

@@ -2058,7 +2076,7 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
if (map_chg || avoid_reserve) {
gbl_chg = hugepage_subpool_get_pages(spool, 1);
if (gbl_chg < 0) {
- vma_end_reservation(h, vma, addr);
+ vma_end_reservation(h, vma, addr, regions_needed);
return ERR_PTR(-ENOSPC);
}

@@ -2105,7 +2123,7 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,

set_page_private(page, (unsigned long)spool);

- map_commit = vma_commit_reservation(h, vma, addr);
+ map_commit = vma_commit_reservation(h, vma, addr, regions_needed);
if (unlikely(map_chg > map_commit)) {
/*
* The page was added to the reservation map between
@@ -2129,7 +2147,7 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
out_subpool_put:
if (map_chg || avoid_reserve)
hugepage_subpool_put_pages(spool, 1);
- vma_end_reservation(h, vma, addr);
+ vma_end_reservation(h, vma, addr, regions_needed);
return ERR_PTR(-ENOSPC);
}

@@ -3850,6 +3868,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
spinlock_t *ptl;
unsigned long haddr = address & huge_page_mask(h);
bool new_page = false;
+ long regions_needed = 0;

/*
* Currently, we are forced to kill the process in the event the
@@ -3967,12 +3986,12 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
* the spinlock.
*/
if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
- if (vma_needs_reservation(h, vma, haddr) < 0) {
+ if (vma_needs_reservation(h, vma, haddr, &regions_needed) < 0) {
ret = VM_FAULT_OOM;
goto backout_unlocked;
}
/* Just decrements count, does not deallocate */
- vma_end_reservation(h, vma, haddr);
+ vma_end_reservation(h, vma, haddr, regions_needed);
}

ptl = huge_pte_lock(h, mm, ptep);
@@ -4062,6 +4081,7 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
struct address_space *mapping;
int need_wait_lock = 0;
unsigned long haddr = address & huge_page_mask(h);
+ long regions_needed = 0;

ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
if (ptep) {
@@ -4116,12 +4136,12 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
* consumed.
*/
if ((flags & FAULT_FLAG_WRITE) && !huge_pte_write(entry)) {
- if (vma_needs_reservation(h, vma, haddr) < 0) {
+ if (vma_needs_reservation(h, vma, haddr, &regions_needed) < 0) {
ret = VM_FAULT_OOM;
goto out_mutex;
}
/* Just decrements count, does not deallocate */
- vma_end_reservation(h, vma, haddr);
+ vma_end_reservation(h, vma, haddr, regions_needed);

if (!(vma->vm_flags & VM_MAYSHARE))
pagecache_page = hugetlbfs_pagecache_page(h,
@@ -4584,7 +4604,7 @@ int hugetlb_reserve_pages(struct inode *inode,
struct hugepage_subpool *spool = subpool_inode(inode);
struct resv_map *resv_map;
struct hugetlb_cgroup *h_cg;
- long gbl_reserve;
+ long gbl_reserve, regions_needed = 0;

/* This should never happen */
if (from > to) {
@@ -4614,7 +4634,7 @@ int hugetlb_reserve_pages(struct inode *inode,
*/
resv_map = inode_resv_map(inode);

- chg = region_chg(resv_map, from, to);
+ chg = region_chg(resv_map, from, to, &regions_needed);

} else {
/* Private mapping. */
@@ -4684,7 +4704,7 @@ int hugetlb_reserve_pages(struct inode *inode,
* else has to be done for private mappings here
*/
if (!vma || vma->vm_flags & VM_MAYSHARE) {
- long add = region_add(resv_map, from, to);
+ long add = region_add(resv_map, from, to, regions_needed);

if (unlikely(chg > add)) {
/*
@@ -4706,7 +4726,7 @@ int hugetlb_reserve_pages(struct inode *inode,
if (!vma || vma->vm_flags & VM_MAYSHARE)
/* Don't call region_abort if region_chg failed */
if (chg >= 0)
- region_abort(resv_map, from, to);
+ region_abort(resv_map, from, to, regions_needed);
if (vma && is_vma_resv_set(vma, HPAGE_RESV_OWNER))
kref_put(&resv_map->refs, resv_map_release);
return ret;
@@ -5130,3 +5150,21 @@ void move_hugetlb_state(struct page *oldpage, struct page *newpage, int reason)
spin_unlock(&hugetlb_lock);
}
}
+
+static struct file_region *
+get_file_region_entry_from_cache(struct resv_map *resv, long from, long to)
+{
+ struct file_region *nrg = NULL;
+
+ VM_BUG_ON(resv->region_cache_count <= 0);
+
+ resv->region_cache_count--;
+ nrg = list_first_entry(&resv->region_cache, struct file_region, link);
+ VM_BUG_ON(!nrg);
+ list_del(&nrg->link);
+
+ nrg->from = from;
+ nrg->to = to;
+
+ return nrg;
+}
--
2.23.0.700.g56cf767bdb-goog