From: Jan Kara <jack@xxxxxxx> Subject: mm: speed up cancel_dirty_page() for clean pages Patch series "Speed up page cache truncation", v1. When rebasing our enterprise distro to a newer kernel (from 4.4 to 4.12) we have noticed a regression in bonnie++ benchmark when deleting files. Eventually we have tracked this down to a fact that page cache truncation got slower by about 10%. There were both gains and losses in the above interval of kernels but we have been able to identify that commit 83929372f629 "filemap: prepare find and delete operations for huge pages" caused about 10% regression on its own. After some investigation it didn't seem easily possible to fix the regression while maintaining the THP in page cache functionality so we've decided to optimize the page cache truncation path instead to make up for the change. This series is a result of that effort. Patch 1 is an easy speedup of cancel_dirty_page(). Patches 2-6 refactor page cache truncation code so that it is easier to batch radix tree operations. Patch 7 implements batching of deletes from the radix tree which more than makes up for the original regression. This patch (of 7): cancel_dirty_page() does quite some work even for clean pages (fetching of mapping, locking of memcg, atomic bit op on page flags) so it accounts for ~2.5% of cost of truncation of a clean page. That is not much but still dumb for something we don't need at all. Check whether a page is actually dirty and avoid any work if not. Link: http://lkml.kernel.org/r/20171010151937.26984-2-jack@xxxxxxx Signed-off-by: Jan Kara <jack@xxxxxxx> Acked-by: Mel Gorman <mgorman@xxxxxxx> Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxx> Cc: Dave Chinner <david@xxxxxxxxxxxxx> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/mm.h | 8 +++++++- mm/page-writeback.c | 4 ++-- 2 files changed, 9 insertions(+), 3 deletions(-) diff -puN include/linux/mm.h~mm-speedup-cancel_dirty_page-for-clean-pages include/linux/mm.h --- a/include/linux/mm.h~mm-speedup-cancel_dirty_page-for-clean-pages +++ a/include/linux/mm.h @@ -1440,7 +1440,13 @@ void account_page_cleaned(struct page *p struct bdi_writeback *wb); int set_page_dirty(struct page *page); int set_page_dirty_lock(struct page *page); -void cancel_dirty_page(struct page *page); +void __cancel_dirty_page(struct page *page); +static inline void cancel_dirty_page(struct page *page) +{ + /* Avoid atomic ops, locking, etc. when not actually needed. */ + if (PageDirty(page)) + __cancel_dirty_page(page); +} int clear_page_dirty_for_io(struct page *page); int get_cmdline(struct task_struct *task, char *buffer, int buflen); diff -puN mm/page-writeback.c~mm-speedup-cancel_dirty_page-for-clean-pages mm/page-writeback.c --- a/mm/page-writeback.c~mm-speedup-cancel_dirty_page-for-clean-pages +++ a/mm/page-writeback.c @@ -2608,7 +2608,7 @@ EXPORT_SYMBOL(set_page_dirty_lock); * page without actually doing it through the VM. Can you say "ext3 is * horribly ugly"? Thought you could. */ -void cancel_dirty_page(struct page *page) +void __cancel_dirty_page(struct page *page) { struct address_space *mapping = page_mapping(page); @@ -2629,7 +2629,7 @@ void cancel_dirty_page(struct page *page ClearPageDirty(page); } } -EXPORT_SYMBOL(cancel_dirty_page); +EXPORT_SYMBOL(__cancel_dirty_page); /* * Clear a page's dirty flag, while caring for dirty memory accounting. _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
