From: "Huang\, Ying" <email@example.com> To: Johannes Weiner <firstname.lastname@example.org> Cc: "Huang\, Ying" <email@example.com>, Andrew Morton <firstname.lastname@example.org>, <email@example.com>, <firstname.lastname@example.org> Subject: Re: [PATCH -mm -v9 2/3] mm, THP, swap: Check whether THP can be split firstly Date: Thu, 20 Apr 2017 08:50:43 +0800 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <20170419161318.GC3376@cmpxchg.org> (Johannes Weiner's message of "Wed, 19 Apr 2017 12:13:18 -0400") Johannes Weiner <firstname.lastname@example.org> writes: > On Wed, Apr 19, 2017 at 03:06:24PM +0800, Huang, Ying wrote: >> From: Huang Ying <email@example.com> >> >> To swap out THP (Transparent Huage Page), before splitting the THP, >> the swap cluster will be allocated and the THP will be added into the >> swap cache. But it is possible that the THP cannot be split, so that >> we must delete the THP from the swap cache and free the swap cluster. >> To avoid that, in this patch, whether the THP can be split is checked >> firstly. The check can only be done racy, but it is good enough for >> most cases. >> >> With the patchset, the swap out throughput improves 3.6% (from about >> 4.16GB/s to about 4.31GB/s) in the vm-scalability swap-w-seq test case >> with 8 processes. The test is done on a Xeon E5 v3 system. The swap >> device used is a RAM simulated PMEM (persistent memory) device. To >> test the sequential swapping out, the test case creates 8 processes, >> which sequentially allocate and write to the anonymous pages until the >> RAM and part of the swap device is used up. >> >> Cc: Johannes Weiner <firstname.lastname@example.org> >> Signed-off-by: "Huang, Ying" <email@example.com> >> Acked-by: Kirill A. Shutemov <firstname.lastname@example.org> [for can_split_huge_page()] > > How often does this actually happen in practice? Because all that this > protects us from is trying to allocate a swap cluster - which with the > si->free_clusters list really isn't all that expensive - and return it > again. Unless this happens all the time in practice, this optimization > seems misplaced. In addition to allocate/free swap cluster, add/delete to/from the swap cache will be called too. > It's especially a little strange because in the other email I asked > about the need for unlikely() annotations, yet this patch is adding > branches and checks for what seems to be an unlikely condition into > the THP hot path. > > I'd suggest you drop both these optimization attempts unless there is > real data proving that they have a measurable impact. To my surprise too, I found this patch has measurable impact in my test. The swap out throughput improves 3.6% in the vm-scalability swap-w-seq test case with 8 processes. Details are in the original patch description. Best Regards, Huang, Ying
next prev parent reply other threads:[~2017-04-20 0:50 UTC|newest] Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-04-19 7:06 [PATCH -mm -v9 0/3] THP swap: Delay splitting THP during swapping out Huang, Ying 2017-04-19 7:06 ` [PATCH -mm -v9 1/3] mm, THP, swap: Delay splitting THP during swap out Huang, Ying 2017-04-19 15:52 ` Johannes Weiner 2017-04-20 0:43 ` Huang, Ying 2017-04-21 6:11 ` Balbir Singh 2017-04-21 7:21 ` Huang, Ying 2017-04-21 14:08 ` Johannes Weiner 2017-04-22 0:07 ` Huang, Ying 2017-04-19 7:06 ` [PATCH -mm -v9 2/3] mm, THP, swap: Check whether THP can be split firstly Huang, Ying 2017-04-19 16:13 ` Johannes Weiner 2017-04-20 0:50 ` Huang, Ying [this message] 2017-04-20 20:50 ` Johannes Weiner 2017-04-21 0:34 ` Huang, Ying 2017-04-19 7:06 ` [PATCH -mm -v9 3/3] mm, THP, swap: Enable THP swap optimization only if has compound map Huang, Ying 2017-04-19 16:00 ` Johannes Weiner 2017-04-20 0:51 ` Huang, Ying
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 \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --subject='Re: [PATCH -mm -v9 2/3] mm, THP, swap: Check whether THP can be split firstly' \ /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 a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).