From: Dave Chinner <email@example.com> To: Jan Kara <firstname.lastname@example.org> Cc: Dave Hansen <email@example.com>, Andi Kleen <firstname.lastname@example.org>, email@example.com, Mel Gorman <firstname.lastname@example.org>, "Kirill A. Shutemov" <email@example.com>, firstname.lastname@example.org Subject: Re: [PATCH 0/7 v1] Speed up page cache truncation Date: Thu, 12 Oct 2017 08:24:01 +1100 [thread overview] Message-ID: <20171011212401.GM15067@dastard> (raw) In-Reply-To: <20171011210613.GQ3667@quack2.suse.cz> On Wed, Oct 11, 2017 at 11:06:13PM +0200, Jan Kara wrote: > On Wed 11-10-17 10:34:47, Dave Hansen wrote: > > On 10/11/2017 01:06 AM, Jan Kara wrote: > > >>> 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. > > >> It's odd that just checking if some pages are huge should be that > > >> expensive, but ok .. > > > Yeah, I was surprised as well but profiles were pretty clear on this - part > > > of the slowdown was caused by loads of page->_compound_head (PageTail() > > > and page_compound() use that) which we previously didn't have to load at > > > all, part was in hpage_nr_pages() function and its use. > > > > Well, page->_compound_head is part of the same cacheline as the rest of > > the page, and the page is surely getting touched during truncation at > > _some_ point. The hpage_nr_pages() might cause the cacheline to get > > loaded earlier than before, but I can't imagine that it's that expensive. > > Then my intuition matches yours ;) but profiles disagree. Do you get the same benefit across different filesystems? > That being said > I'm not really expert in CPU microoptimizations and profiling so feel free > to gather perf profiles yourself before and after commit 83929372f629 and > get better explanation of where the cost is - I would be really curious > what you come up with because the explanation I have disagrees with my > intuition as well... When I see this sort of stuff my immediate thought is "what is the change in the icache footprint of the hot codepath"? There's a few IO benchmarks (e.g. IOZone) that are l1/l2 cache footprint sensitive on XFS, and can see up to 10% differences in performance from kernel build to kernel build that have no code changes in the IO paths or l1/l2 dcache footprint. Cheers, Dave. -- Dave Chinner email@example.com -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to firstname.lastname@example.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"email@example.com"> firstname.lastname@example.org </a>
next prev parent reply other threads:[~2017-10-11 21:24 UTC|newest] Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-10-10 15:19 Jan Kara 2017-10-10 15:19 ` Jan Kara 2017-10-10 15:19 ` [PATCH 1/7] mm: Speedup cancel_dirty_page() for clean pages Jan Kara 2017-10-10 15:19 ` Jan Kara 2017-10-10 15:19 ` [PATCH 2/7] mm: Refactor truncate_complete_page() Jan Kara 2017-10-10 15:19 ` Jan Kara 2017-10-10 15:19 ` [PATCH 3/7] mm: Factor out page cache page freeing into a separate function Jan Kara 2017-10-10 15:19 ` Jan Kara 2017-10-10 15:19 ` [PATCH 4/7] mm: Move accounting updates before page_cache_tree_delete() Jan Kara 2017-10-10 15:19 ` Jan Kara 2017-10-10 15:19 ` [PATCH 5/7] mm: Move clearing of page->mapping to page_cache_tree_delete() Jan Kara 2017-10-10 15:19 ` Jan Kara 2017-10-10 15:19 ` [PATCH 6/7] mm: Factor out checks and accounting from __delete_from_page_cache() Jan Kara 2017-10-10 15:19 ` Jan Kara 2017-10-10 15:19 ` [PATCH 7/7] mm: Batch radix tree operations when truncating pages Jan Kara 2017-10-10 15:19 ` Jan Kara 2017-10-11 7:39 ` Mel Gorman 2017-10-17 23:05 ` Andrew Morton 2017-10-17 23:05 ` Andrew Morton 2017-10-18 10:44 ` Jan Kara 2017-10-10 17:25 ` [PATCH 0/7 v1] Speed up page cache truncation Andi Kleen 2017-10-10 17:25 ` Andi Kleen 2017-10-11 8:06 ` Jan Kara 2017-10-11 16:51 ` Andi Kleen 2017-10-11 17:34 ` Dave Hansen 2017-10-11 17:59 ` Mel Gorman 2017-10-11 18:37 ` Andi Kleen 2017-10-11 21:06 ` Jan Kara 2017-10-11 21:24 ` Dave Chinner [this message] 2017-10-12 9:09 ` Mel Gorman 2017-10-12 14:07 ` Jan Kara
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20171011212401.GM15067@dastard \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --subject='Re: [PATCH 0/7 v1] Speed up page cache truncation' \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.