[PATCH v7 5/9] hugetlb: disable region_add file_region coalescing

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@google.com

---

Changes in v7: - region_chg no longer allocates (t-f) / 2 file_region entries. Changes in v6: - Fix bug in number of region_caches allocated by region_chg

--- mm/hugetlb.c | 327 ++++++++++++++++++++++++++++++++------------------- 1 file changed, 205 insertions(+), 122 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 8d8aa89a9928e..3d98e1b771390 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -244,107 +244,138 @@ 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. + * list. If regions_needed != NULL and count_only == true, then regions_needed + * will indicate the number of file_regions needed in the cache to carry out to + * add the regions for this range. */ static long add_reservation_in_range(struct resv_map *resv, long f, long t, - bool count_only) + long *regions_needed, 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; + if (regions_needed) + *regions_needed = 0;

- 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); + } else if (regions_needed) + *regions_needed += 1; } - 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); + } else if (regions_needed) + *regions_needed += 1; + last_accounted_offset = t; }

- return chg; + return add; }

/* * Add the huge page range represented by [f, t) to the reserve - * map. Existing regions will be expanded to accommodate the specified - * range, or a region will be taken from the cache. Sufficient regions - * must exist in the cache due to the previous call to region_chg with - * the same range. + * map. Regions will be taken from the cache to fill in this range. + * Sufficient regions should exist in the cache due to the previous + * call to region_chg with the same range, but in some cases the cache will not + * have sufficient entries. The extra needed entries will be allocated. + * + * 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. + * Return the number of new huge pages added to the map. This number is greater + * than or equal to zero. If file_region entries needed to be allocated for + * this operation and we were not able to allocate, it ruturns -ENOMEM. + * region_add of regions of length 1 never allocate file_regions and cannot + * fail. */ -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 in_regions_needed) { - struct list_head *head = &resv->regions; - struct file_region *rg, *nrg; - long add = 0; + long add = 0, actual_regions_needed = 0; + struct file_region *trg = NULL;

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; +retry: + + /* Count how many regions are actually needed to execute this add. */ + add_reservation_in_range(resv, f, t, &actual_regions_needed, true);

/* - * 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. + * Check for sufficient descriptors in the cache to accommodate + * this add operation. */ - 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); + if (resv->region_cache_count < actual_regions_needed) { + /* region_add operation of range 1 should never need to + * allocate file_region entries. + */ + VM_BUG_ON(t - f <= 1); + while (resv->region_cache_count < actual_regions_needed) { + /* Must drop lock to allocate a new descriptor. */ + spin_unlock(&resv->lock); + trg = kmalloc(sizeof(*trg), GFP_KERNEL); + if (!trg) + return -ENOMEM; + + spin_lock(&resv->lock); + list_add(&trg->link, &resv->region_cache); + resv->region_cache_count++; + }

- add += t - f; - goto out_locked; + goto retry; }

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

-out_locked: - resv->adds_in_progress--; spin_unlock(&resv->lock); VM_BUG_ON(add < 0); return add; @@ -361,31 +392,38 @@ 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->adds_in_progress. 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;

spin_lock(&resv->lock); -retry_locked: - resv->adds_in_progress++; + + /* Count how many hugepages in this range are NOT respresented. */ + chg = add_reservation_in_range(resv, f, t, out_regions_needed, true); + + if (*out_regions_needed < 1) + *out_regions_needed = 1; + + 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; @@ -393,11 +431,8 @@ 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; }

- chg = add_reservation_in_range(resv, f, t, true); - spin_unlock(&resv->lock); return chg; } @@ -407,17 +442,20 @@ 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); }

@@ -1897,9 +1935,10 @@ 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; @@ -1912,20 +1951,28 @@ 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); + /* region_add calls of range 1 should never fail. */ + VM_BUG_ON(ret < 0); 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: - if (vma->vm_flags & VM_MAYSHARE) - ret = region_add(resv, idx, idx + 1); - else { - region_abort(resv, idx, idx + 1); + VM_BUG_ON(in_regions_needed == -1); + if (vma->vm_flags & VM_MAYSHARE) { + ret = region_add(resv, idx, idx + 1, in_regions_needed); + /* region_add calls of range 1 should never fail. */ + VM_BUG_ON(ret < 0); + } else { + region_abort(resv, idx, idx + 1, in_regions_needed); ret = region_del(resv, idx, idx + 1); } break; @@ -1958,28 +2005,32 @@ 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); }

/* @@ -1997,8 +2048,10 @@ 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)) { /* @@ -2014,7 +2067,8 @@ 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 @@ -2022,7 +2076,7 @@ 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); } }

@@ -2036,6 +2090,7 @@ 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); /* @@ -2043,7 +2098,8 @@ 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);

@@ -2057,7 +2113,7 @@ 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); }

@@ -2104,7 +2160,7 @@ 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 @@ -2128,7 +2184,7 @@ 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); }

@@ -3849,6 +3905,7 @@ 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 @@ -3966,12 +4023,12 @@ 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); @@ -4061,6 +4118,7 @@ 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) { @@ -4115,12 +4173,12 @@ 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, @@ -4578,12 +4636,12 @@ int hugetlb_reserve_pages(struct inode *inode, struct vm_area_struct *vma, vm_flags_t vm_flags) { - long ret, chg; + long ret, chg, add; struct hstate *h = hstate_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) { @@ -4613,7 +4671,7 @@ 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. */ @@ -4683,9 +4741,14 @@ 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); - - if (unlikely(chg > add)) { + add = region_add(resv_map, from, to, regions_needed); + + if (unlikely(add < 0)) { + hugetlb_acct_memory(h, -gbl_reserve); + /* put back original number of pages, chg */ + (void)hugepage_subpool_put_pages(spool, chg); + goto out_err; + } else if (unlikely(chg > add)) { /* * pages in this range were added to the reserve * map between region_chg and region_add. This @@ -4703,9 +4766,11 @@ int hugetlb_reserve_pages(struct inode *inode, return 0; out_err: 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); + /* Only call region_abort if the region_chg succeeded but the + * region_add failed. + */ + if (chg >= 0 && add < 0) + 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; @@ -5129,3 +5194,21 @@ 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; +} -- 2.24.0.rc0.303.g954a862665-goog