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Mon, 14 Sep 2020 13:00:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Transfer-Encoding:MIME-Version: References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From:Sender:Reply-To: Content-Type:Content-ID:Content-Description; bh=PMOVyDdKtjZVle1vj+CLG+zoWJ/Fx9rNqdgIHXqb7pc=; b=glycpH4Qa6n1JZz0u6NJ8BbEGS BrENBaCSXSRnFcqYmid9IdPPK9xUrAFYfkFbBFZBbZVz1DTZr8IbUGdp3D7vkcCgfRU2L2p0pXbvH c8LJJtl6tQga73ct2BG4877bo0hmHqxNtB+o/LWLV8BX04P2H8UVMZZr274hyZnAgmFQCeVSdpaaL XuFPElNjsiZ1qqajEveS3lkFvlU8zDj0XK1TtTNHp3iUuS0Nb3snoBAxPKXNAJITsK2DzLR/p2+WN gdQljTY0msCc8ShtwidKRvo/QgMwmuKijVYJCQP02nYeWMwvf6AEijy1Gio8YA/yfpmMdtNgq7+wv 70NUHsEQ==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kHo6B-00030k-02; Mon, 14 Sep 2020 13:00:47 +0000 From: "Matthew Wilcox (Oracle)" To: linux-mm@kvack.org Cc: "Matthew Wilcox (Oracle)" , Andrew Morton , Hugh Dickins , William Kucharski , Johannes Weiner , Jan Kara , Yang Shi , Dave Chinner , linux-kernel@vger.kernel.org Subject: [PATCH v2 11/12] mm/truncate,shmem: Handle truncates that split THPs Date: Mon, 14 Sep 2020 14:00:41 +0100 Message-Id: <20200914130042.11442-12-willy@infradead.org> X-Mailer: git-send-email 2.21.3 In-Reply-To: <20200914130042.11442-1-willy@infradead.org> References: <20200914130042.11442-1-willy@infradead.org> MIME-Version: 1.0 X-Rspamd-Queue-Id: 4190E18013206 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Handle THP 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_page(). We lose the easy 'bail out' path if a truncate or hole punch is entirely within a single page. We can add some more complex logic to restore the optimisation if it proves to be worthwhile. Signed-off-by: Matthew Wilcox (Oracle) --- mm/internal.h | 1 + mm/shmem.c | 98 +++++++++++++++-------------------------- mm/truncate.c | 119 +++++++++++++++++++++++++++++++------------------- 3 files changed, 110 insertions(+), 108 deletions(-) diff --git a/mm/internal.h b/mm/internal.h index 1c5f4425ed74..d17d9060902f 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -620,4 +620,5 @@ struct migration_target_control { gfp_t gfp_mask; }; +bool truncate_inode_partial_page(struct page *page, loff_t start, loff_t end); #endif /* __MM_INTERNAL_H */ diff --git a/mm/shmem.c b/mm/shmem.c index b2b94025841a..23bb79ec070f 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -855,32 +855,6 @@ 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) -{ - if (!PageTransCompound(page)) - return true; - - /* 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; -} - /* * Remove range of pages and swap entries from page cache, and free them. * If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate. @@ -892,10 +866,9 @@ 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 pagevec pvec; pgoff_t indices[PAGEVEC_SIZE]; + struct page *page; long nr_swaps_freed = 0; pgoff_t index; int i; @@ -908,7 +881,7 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, while (index < end && find_lock_entries(mapping, index, end - 1, &pvec, indices)) { for (i = 0; i < pagevec_count(&pvec); i++) { - struct page *page = pvec.pages[i]; + page = pvec.pages[i]; index = indices[i]; @@ -931,33 +904,39 @@ 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); + index = -1; + if (end != -1 && ((lend + 1) % PAGE_SIZE)) + index = lend >> PAGE_SHIFT; + page = NULL; + shmem_getpage(inode, lstart >> PAGE_SHIFT, &page, SGP_READ); + if (page) { + bool same_page; + + page = thp_head(page); + same_page = lend + 1 < page_offset(page) + thp_size(page); + if (same_page) + index = -1; + set_page_dirty(page); + if (!truncate_inode_partial_page(page, lstart, lend)) { + start = page->index + thp_nr_pages(page); + if (same_page) + end = page->index; } + unlock_page(page); + put_page(page); + page = NULL; } - if (partial_end) { - struct page *page = NULL; + + if (index != -1) 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 (page) { + page = thp_head(page); + set_page_dirty(page); + if (!truncate_inode_partial_page(page, lstart, lend)) + end = page->index; + unlock_page(page); + put_page(page); } - if (start >= end) - return; index = start; while (index < end) { @@ -973,7 +952,7 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, continue; } for (i = 0; i < pagevec_count(&pvec); i++) { - struct page *page = pvec.pages[i]; + page = pvec.pages[i]; index = indices[i]; if (xa_is_value(page)) { @@ -998,18 +977,9 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, break; } VM_BUG_ON_PAGE(PageWriteback(page), page); - if (shmem_punch_compound(page, start, end)) - truncate_inode_page(mapping, page); - else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { - /* Wipe the page and don't get stuck */ - clear_highpage(page); - flush_dcache_page(page); - set_page_dirty(page); - if (index < - round_up(start, HPAGE_PMD_NR)) - start = index + 1; - } + truncate_inode_page(mapping, page); } + index = page->index + thp_nr_pages(page) - 1; unlock_page(page); } pagevec_remove_exceptionals(&pvec); diff --git a/mm/truncate.c b/mm/truncate.c index d62aeffbffcc..06ed2f93069d 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -224,6 +224,53 @@ int truncate_inode_page(struct address_space *mapping, struct page *page) return 0; } +/* + * Handle partial (transparent) pages. The page may be entirely within the + * range if a split has raced with us. If not, we zero the part of the + * page that's within the (start, end] range, and then split the page if + * it's a THP. 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 THP splitting failed so the caller can can avoid + * discarding the entire page which is stubbornly unsplit. + */ +bool truncate_inode_partial_page(struct page *page, loff_t start, loff_t end) +{ + loff_t pos = page_offset(page); + unsigned int offset, length; + + if (pos < start) + offset = start - pos; + else + offset = 0; + length = thp_size(page); + if (pos + length <= (u64)end) + length = length - offset; + else + length = end + 1 - pos - offset; + + wait_on_page_writeback(page); + if (length == thp_size(page)) { + truncate_inode_page(page->mapping, page); + 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. + */ + zero_user(page, offset, length); + + cleancache_invalidate_page(page->mapping, page); + if (page_has_private(page)) + do_invalidatepage(page, offset, length); + if (!PageTransHuge(page)) + return true; + return split_huge_page(page) == 0; +} + /* * Used to get rid of pages on hardware memory corruption. */ @@ -288,20 +335,15 @@ 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 pagevec pvec; pgoff_t indices[PAGEVEC_SIZE]; pgoff_t index; int i; + struct page * page; if (mapping->nrpages == 0 && mapping->nrexceptional == 0) 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 @@ -334,48 +376,37 @@ 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); + index = -1; + if (end != -1 && ((lend + 1) % PAGE_SIZE)) + index = lend >> PAGE_SHIFT; + page = find_lock_head(mapping, lstart >> PAGE_SHIFT); + if (page) { + bool same_page = lend + 1 < page_offset(page) + thp_size(page); + if (same_page) + index = -1; + if (!truncate_inode_partial_page(page, lstart, lend)) { + start = page->index + thp_nr_pages(page); + if (same_page) + end = page->index; } + unlock_page(page); + put_page(page); + page = 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 (index != -1) + page = find_lock_head(mapping, index); + if (page) { + if (!truncate_inode_partial_page(page, lstart, lend)) + end = page->index; + unlock_page(page); + put_page(page); } - /* - * 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, &pvec, indices)) { /* If all gone from start onwards, we're done */ @@ -387,7 +418,7 @@ void truncate_inode_pages_range(struct address_space *mapping, } for (i = 0; i < pagevec_count(&pvec); i++) { - struct page *page = pvec.pages[i]; + page = pvec.pages[i]; /* We rely upon deletion not changing page->index */ index = indices[i]; @@ -396,7 +427,7 @@ void truncate_inode_pages_range(struct address_space *mapping, continue; lock_page(page); - WARN_ON(page_to_index(page) != index); + index = page->index + thp_nr_pages(page) - 1; wait_on_page_writeback(page); truncate_inode_page(mapping, page); unlock_page(page);