From b9a8a4195c7d3a51235a4fc974a46ad4e9689ffd Mon Sep 17 00:00:00 2001 From: "Matthew Wilcox (Oracle)" Date: Wed, 27 May 2020 17:59:22 -0400 Subject: [PATCH] truncate,shmem: Handle truncates that split large folios Handle folio splitting in the parts of the truncation functions which already handle partial pages. Factor all that code out into a new function called truncate_inode_partial_folio(). Signed-off-by: Matthew Wilcox (Oracle) Reviewed-by: Jan Kara Reviewed-by: William Kucharski --- mm/internal.h | 2 + mm/shmem.c | 108 +++++++++++++++++++--------------------------- mm/truncate.c | 117 ++++++++++++++++++++++++++++++++------------------ 3 files changed, 122 insertions(+), 105 deletions(-) diff --git a/mm/internal.h b/mm/internal.h index c52c05dc6b1f..26af8a5a5be3 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -98,6 +98,8 @@ unsigned find_get_entries(struct address_space *mapping, pgoff_t start, pgoff_t end, struct folio_batch *fbatch, pgoff_t *indices); void filemap_free_folio(struct address_space *mapping, struct folio *folio); int truncate_inode_folio(struct address_space *mapping, struct folio *folio); +bool truncate_inode_partial_folio(struct folio *folio, loff_t start, + loff_t end); /** * folio_evictable - Test whether a folio is evictable. diff --git a/mm/shmem.c b/mm/shmem.c index bbfa2d05e787..e4c9e5c7081f 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -880,30 +880,26 @@ void shmem_unlock_mapping(struct address_space *mapping) } } -/* - * Check whether a hole-punch or truncation needs to split a huge page, - * returning true if no split was required, or the split has been successful. - * - * Eviction (or truncation to 0 size) should never need to split a huge page; - * but in rare cases might do so, if shmem_undo_range() failed to trylock on - * head, and then succeeded to trylock on tail. - * - * A split can only succeed when there are no additional references on the - * huge page: so the split below relies upon find_get_entries() having stopped - * when it found a subpage of the huge page, without getting further references. - */ -static bool shmem_punch_compound(struct page *page, pgoff_t start, pgoff_t end) +static struct folio *shmem_get_partial_folio(struct inode *inode, pgoff_t index) { - if (!PageTransCompound(page)) - return true; + struct folio *folio; + struct page *page; - /* Just proceed to delete a huge page wholly within the range punched */ - if (PageHead(page) && - page->index >= start && page->index + HPAGE_PMD_NR <= end) - return true; - - /* Try to split huge page, so we can truly punch the hole or truncate */ - return split_huge_page(page) >= 0; + /* + * At first avoid shmem_getpage(,,,SGP_READ): that fails + * beyond i_size, and reports fallocated pages as holes. + */ + folio = __filemap_get_folio(inode->i_mapping, index, + FGP_ENTRY | FGP_LOCK, 0); + if (!xa_is_value(folio)) + return folio; + /* + * But read a page back from swap if any of it is within i_size + * (although in some cases this is just a waste of time). + */ + page = NULL; + shmem_getpage(inode, index, &page, SGP_READ); + return page ? page_folio(page) : NULL; } /* @@ -917,10 +913,10 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, struct shmem_inode_info *info = SHMEM_I(inode); pgoff_t start = (lstart + PAGE_SIZE - 1) >> PAGE_SHIFT; pgoff_t end = (lend + 1) >> PAGE_SHIFT; - unsigned int partial_start = lstart & (PAGE_SIZE - 1); - unsigned int partial_end = (lend + 1) & (PAGE_SIZE - 1); struct folio_batch fbatch; pgoff_t indices[PAGEVEC_SIZE]; + struct folio *folio; + bool same_folio; long nr_swaps_freed = 0; pgoff_t index; int i; @@ -936,7 +932,7 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, while (index < end && find_lock_entries(mapping, index, end - 1, &fbatch, indices)) { for (i = 0; i < folio_batch_count(&fbatch); i++) { - struct folio *folio = fbatch.folios[i]; + folio = fbatch.folios[i]; index = indices[i]; @@ -959,33 +955,30 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, index++; } - if (partial_start) { - struct page *page = NULL; - shmem_getpage(inode, start - 1, &page, SGP_READ); - if (page) { - unsigned int top = PAGE_SIZE; - if (start > end) { - top = partial_end; - partial_end = 0; - } - zero_user_segment(page, partial_start, top); - set_page_dirty(page); - unlock_page(page); - put_page(page); + same_folio = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT); + folio = shmem_get_partial_folio(inode, lstart >> PAGE_SHIFT); + if (folio) { + same_folio = lend < folio_pos(folio) + folio_size(folio); + folio_mark_dirty(folio); + if (!truncate_inode_partial_folio(folio, lstart, lend)) { + start = folio->index + folio_nr_pages(folio); + if (same_folio) + end = folio->index; } + folio_unlock(folio); + folio_put(folio); + folio = NULL; } - if (partial_end) { - struct page *page = NULL; - shmem_getpage(inode, end, &page, SGP_READ); - if (page) { - zero_user_segment(page, 0, partial_end); - set_page_dirty(page); - unlock_page(page); - put_page(page); - } + + if (!same_folio) + folio = shmem_get_partial_folio(inode, lend >> PAGE_SHIFT); + if (folio) { + folio_mark_dirty(folio); + if (!truncate_inode_partial_folio(folio, lstart, lend)) + end = folio->index; + folio_unlock(folio); + folio_put(folio); } - if (start >= end) - return; index = start; while (index < end) { @@ -1001,7 +994,7 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, continue; } for (i = 0; i < folio_batch_count(&fbatch); i++) { - struct folio *folio = fbatch.folios[i]; + folio = fbatch.folios[i]; index = indices[i]; if (xa_is_value(folio)) { @@ -1019,8 +1012,6 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, folio_lock(folio); if (!unfalloc || !folio_test_uptodate(folio)) { - struct page *page = folio_file_page(folio, - index); if (folio_mapping(folio) != mapping) { /* Page was replaced by swap: retry */ folio_unlock(folio); @@ -1029,18 +1020,9 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, } VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio); - if (shmem_punch_compound(page, start, end)) - truncate_inode_folio(mapping, folio); - else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { - /* Wipe the page and don't get stuck */ - clear_highpage(page); - flush_dcache_page(page); - folio_mark_dirty(folio); - if (index < - round_up(start, HPAGE_PMD_NR)) - start = index + 1; - } + truncate_inode_folio(mapping, folio); } + index = folio->index + folio_nr_pages(folio) - 1; folio_unlock(folio); } folio_batch_remove_exceptionals(&fbatch); diff --git a/mm/truncate.c b/mm/truncate.c index 2d1dae085acb..5c87cdc70e7b 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -228,6 +228,58 @@ int truncate_inode_folio(struct address_space *mapping, struct folio *folio) return 0; } +/* + * Handle partial folios. The folio may be entirely within the + * range if a split has raced with us. If not, we zero the part of the + * folio that's within the [start, end] range, and then split the folio if + * it's large. split_page_range() will discard pages which now lie beyond + * i_size, and we rely on the caller to discard pages which lie within a + * newly created hole. + * + * Returns false if splitting failed so the caller can avoid + * discarding the entire folio which is stubbornly unsplit. + */ +bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) +{ + loff_t pos = folio_pos(folio); + unsigned int offset, length; + + if (pos < start) + offset = start - pos; + else + offset = 0; + length = folio_size(folio); + if (pos + length <= (u64)end) + length = length - offset; + else + length = end + 1 - pos - offset; + + folio_wait_writeback(folio); + if (length == folio_size(folio)) { + truncate_inode_folio(folio->mapping, folio); + return true; + } + + /* + * We may be zeroing pages we're about to discard, but it avoids + * doing a complex calculation here, and then doing the zeroing + * anyway if the page split fails. + */ + folio_zero_range(folio, offset, length); + + cleancache_invalidate_page(folio->mapping, &folio->page); + if (folio_has_private(folio)) + do_invalidatepage(&folio->page, offset, length); + if (!folio_test_large(folio)) + return true; + if (split_huge_page(&folio->page) == 0) + return true; + if (folio_test_dirty(folio)) + return false; + truncate_inode_folio(folio->mapping, folio); + return true; +} + /* * Used to get rid of pages on hardware memory corruption. */ @@ -294,20 +346,16 @@ void truncate_inode_pages_range(struct address_space *mapping, { pgoff_t start; /* inclusive */ pgoff_t end; /* exclusive */ - unsigned int partial_start; /* inclusive */ - unsigned int partial_end; /* exclusive */ struct folio_batch fbatch; pgoff_t indices[PAGEVEC_SIZE]; pgoff_t index; int i; + struct folio *folio; + bool same_folio; if (mapping_empty(mapping)) goto out; - /* Offsets within partial pages */ - partial_start = lstart & (PAGE_SIZE - 1); - partial_end = (lend + 1) & (PAGE_SIZE - 1); - /* * 'start' and 'end' always covers the range of pages to be fully * truncated. Partial pages are covered with 'partial_start' at the @@ -340,47 +388,32 @@ void truncate_inode_pages_range(struct address_space *mapping, cond_resched(); } - if (partial_start) { - struct page *page = find_lock_page(mapping, start - 1); - if (page) { - unsigned int top = PAGE_SIZE; - if (start > end) { - /* Truncation within a single page */ - top = partial_end; - partial_end = 0; - } - wait_on_page_writeback(page); - zero_user_segment(page, partial_start, top); - cleancache_invalidate_page(mapping, page); - if (page_has_private(page)) - do_invalidatepage(page, partial_start, - top - partial_start); - unlock_page(page); - put_page(page); + same_folio = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT); + folio = __filemap_get_folio(mapping, lstart >> PAGE_SHIFT, FGP_LOCK, 0); + if (folio) { + same_folio = lend < folio_pos(folio) + folio_size(folio); + if (!truncate_inode_partial_folio(folio, lstart, lend)) { + start = folio->index + folio_nr_pages(folio); + if (same_folio) + end = folio->index; } + folio_unlock(folio); + folio_put(folio); + folio = NULL; } - if (partial_end) { - struct page *page = find_lock_page(mapping, end); - if (page) { - wait_on_page_writeback(page); - zero_user_segment(page, 0, partial_end); - cleancache_invalidate_page(mapping, page); - if (page_has_private(page)) - do_invalidatepage(page, 0, - partial_end); - unlock_page(page); - put_page(page); - } + + if (!same_folio) + folio = __filemap_get_folio(mapping, lend >> PAGE_SHIFT, + FGP_LOCK, 0); + if (folio) { + if (!truncate_inode_partial_folio(folio, lstart, lend)) + end = folio->index; + folio_unlock(folio); + folio_put(folio); } - /* - * If the truncation happened within a single page no pages - * will be released, just zeroed, so we can bail out now. - */ - if (start >= end) - goto out; index = start; - for ( ; ; ) { + while (index < end) { cond_resched(); if (!find_get_entries(mapping, index, end - 1, &fbatch, indices)) {