From d144bf6205342a4b5fed5d204ae18849a4de741b Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Thu, 2 Sep 2021 14:54:21 -0700 Subject: [PATCH] huge tmpfs: fix split_huge_page() after FALLOC_FL_KEEP_SIZE A successful shmem_fallocate() guarantees that the extent has been reserved, even beyond i_size when the FALLOC_FL_KEEP_SIZE flag was used. But that guarantee is broken by shmem_unused_huge_shrink()'s attempts to split huge pages and free their excess beyond i_size; and by other uses of split_huge_page() near i_size. It's sad to add a shmem inode field just for this, but I did not find a better way to keep the guarantee. A flag to say KEEP_SIZE has been used would be cheaper, but I'm averse to unclearable flags. The fallocend field is not perfect either (many disjoint ranges might be fallocated), but good enough; and gains another use later on. Link: https://lkml.kernel.org/r/ca9a146-3a59-6cd3-7f28-e9a044bb1052@google.com Fixes: 779750d20b93 ("shmem: split huge pages beyond i_size under memory pressure") Signed-off-by: Hugh Dickins Reviewed-by: Yang Shi Cc: "Kirill A. Shutemov" Cc: Matthew Wilcox Cc: Miaohe Lin Cc: Michal Hocko Cc: Mike Kravetz Cc: Rik van Riel Cc: Shakeel Butt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/shmem_fs.h | 13 +++++++++++++ mm/huge_memory.c | 6 ++++-- mm/shmem.c | 15 ++++++++++++++- 3 files changed, 31 insertions(+), 3 deletions(-) diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h index 0a8499fb9c3c..bfc5899d18e0 100644 --- a/include/linux/shmem_fs.h +++ b/include/linux/shmem_fs.h @@ -18,6 +18,7 @@ struct shmem_inode_info { unsigned long flags; unsigned long alloced; /* data pages alloced to file */ unsigned long swapped; /* subtotal assigned to swap */ + pgoff_t fallocend; /* highest fallocate endindex */ struct list_head shrinklist; /* shrinkable hpage inodes */ struct list_head swaplist; /* chain of maybes on swap */ struct shared_policy policy; /* NUMA memory alloc policy */ @@ -119,6 +120,18 @@ static inline bool shmem_file(struct file *file) return shmem_mapping(file->f_mapping); } +/* + * If fallocate(FALLOC_FL_KEEP_SIZE) has been used, there may be pages + * beyond i_size's notion of EOF, which fallocate has committed to reserving: + * which split_huge_page() must therefore not delete. This use of a single + * "fallocend" per inode errs on the side of not deleting a reservation when + * in doubt: there are plenty of cases when it preserves unreserved pages. + */ +static inline pgoff_t shmem_fallocend(struct inode *inode, pgoff_t eof) +{ + return max(eof, SHMEM_I(inode)->fallocend); +} + extern bool shmem_charge(struct inode *inode, long pages); extern void shmem_uncharge(struct inode *inode, long pages); diff --git a/mm/huge_memory.c b/mm/huge_memory.c index afff3ac87067..890fb73ac89b 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2454,11 +2454,11 @@ static void __split_huge_page(struct page *page, struct list_head *list, for (i = nr - 1; i >= 1; i--) { __split_huge_page_tail(head, i, lruvec, list); - /* Some pages can be beyond i_size: drop them from page cache */ + /* Some pages can be beyond EOF: drop them from page cache */ if (head[i].index >= end) { ClearPageDirty(head + i); __delete_from_page_cache(head + i, NULL); - if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head)) + if (shmem_mapping(head->mapping)) shmem_uncharge(head->mapping->host, 1); put_page(head + i); } else if (!PageAnon(page)) { @@ -2686,6 +2686,8 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) * head page lock is good enough to serialize the trimming. */ end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE); + if (shmem_mapping(mapping)) + end = shmem_fallocend(mapping->host, end); } /* diff --git a/mm/shmem.c b/mm/shmem.c index 9ef579f6cab3..e391325dfc21 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -902,6 +902,9 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, if (lend == -1) end = -1; /* unsigned, so actually very big */ + if (info->fallocend > start && info->fallocend <= end && !unfalloc) + info->fallocend = start; + pagevec_init(&pvec); index = start; while (index < end && find_lock_entries(mapping, index, end - 1, @@ -2650,7 +2653,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset, struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb); struct shmem_inode_info *info = SHMEM_I(inode); struct shmem_falloc shmem_falloc; - pgoff_t start, index, end; + pgoff_t start, index, end, undo_fallocend; int error; if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE)) @@ -2719,6 +2722,15 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset, inode->i_private = &shmem_falloc; spin_unlock(&inode->i_lock); + /* + * info->fallocend is only relevant when huge pages might be + * involved: to prevent split_huge_page() freeing fallocated + * pages when FALLOC_FL_KEEP_SIZE committed beyond i_size. + */ + undo_fallocend = info->fallocend; + if (info->fallocend < end) + info->fallocend = end; + for (index = start; index < end; ) { struct page *page; @@ -2733,6 +2745,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset, else error = shmem_getpage(inode, index, &page, SGP_FALLOC); if (error) { + info->fallocend = undo_fallocend; /* Remove the !PageUptodate pages we added */ if (index > start) { shmem_undo_range(inode,