From: Dave Hansen <dave.hansen@intel.com> To: "Odzioba, Lukasz" <lukasz.odzioba@intel.com>, Michal Hocko <mhocko@kernel.org> Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "Shutemov, Kirill" <kirill.shutemov@intel.com>, "Anaczkowski, Lukasz" <lukasz.anaczkowski@intel.com>, "Shutemov, Kirill" <kirill.shutemov@intel.com> Subject: Re: mm: pages are not freed from lru_add_pvecs after process termination Date: Fri, 6 May 2016 09:04:34 -0700 [thread overview] Message-ID: <572CC092.5020702@intel.com> (raw) In-Reply-To: <D6EDEBF1F91015459DB866AC4EE162CC023C402E@IRSMSX103.ger.corp.intel.com> On 05/06/2016 08:10 AM, Odzioba, Lukasz wrote: > On Thu 05-05-16 09:21:00, Michal Hocko wrote: >> Or maybe the async nature of flushing turns >> out to be just impractical and unreliable and we will end up skipping >> THP (or all compound pages) for pcp LRU add cache. Let's see... > > What if we simply skip lru_add pvecs for compound pages? > That way we still have compound pages on LRU's, but the problem goes > away. It is not quite what this naïve patch does, but it works nice for me. > > diff --git a/mm/swap.c b/mm/swap.c > index 03aacbc..c75d5e1 100644 > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -392,7 +392,9 @@ static void __lru_cache_add(struct page *page) > get_page(page); > if (!pagevec_space(pvec)) > __pagevec_lru_add(pvec); > pagevec_add(pvec, page); > + if (PageCompound(page)) > + __pagevec_lru_add(pvec); > put_cpu_var(lru_add_pvec); > } That's not _quite_ what I had in mind since that drains the entire pvec every time a large page is encountered. But I'm conflicted about what the right behavior _is_. We'd taking the LRU lock for 'page' anyway, so we might as well drain the pvec. Or, does the additional work to put the page on to a pvec and then immediately drain it overwhelm that advantage? Or does it just not matter? Kirill, do you have a suggestion for how we should be checking for THP pages in code like this? PageCompound() will surely _work_ for anon-THP and your file-THP, but is it the best way to check? > Do we have any tests that I could use to measure performance impact > of such changes before I start to tweak it up? Or maybe it doesn't make > sense at all ? You probably want to very carefully calculate the time to fault a page, then separately to free a page. If we can't manage to detect a delta on a little microbenchmark like that then we'll probably never see one in practice. You'll want to measure the fault time for a 4k pages, 2M pages, and then possibly a mix. You'll want to do this in a highly parallel test to make sure any additional LRU lock overhead shows up.
WARNING: multiple messages have this Message-ID (diff)
From: Dave Hansen <dave.hansen@intel.com> To: "Odzioba, Lukasz" <lukasz.odzioba@intel.com>, Michal Hocko <mhocko@kernel.org> Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "Shutemov, Kirill" <kirill.shutemov@intel.com>, "Anaczkowski, Lukasz" <lukasz.anaczkowski@intel.com>"Shutemov, Kirill" <kirill.shutemov@intel.com> Subject: Re: mm: pages are not freed from lru_add_pvecs after process termination Date: Fri, 6 May 2016 09:04:34 -0700 [thread overview] Message-ID: <572CC092.5020702@intel.com> (raw) In-Reply-To: <D6EDEBF1F91015459DB866AC4EE162CC023C402E@IRSMSX103.ger.corp.intel.com> On 05/06/2016 08:10 AM, Odzioba, Lukasz wrote: > On Thu 05-05-16 09:21:00, Michal Hocko wrote: >> Or maybe the async nature of flushing turns >> out to be just impractical and unreliable and we will end up skipping >> THP (or all compound pages) for pcp LRU add cache. Let's see... > > What if we simply skip lru_add pvecs for compound pages? > That way we still have compound pages on LRU's, but the problem goes > away. It is not quite what this naive patch does, but it works nice for me. > > diff --git a/mm/swap.c b/mm/swap.c > index 03aacbc..c75d5e1 100644 > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -392,7 +392,9 @@ static void __lru_cache_add(struct page *page) > get_page(page); > if (!pagevec_space(pvec)) > __pagevec_lru_add(pvec); > pagevec_add(pvec, page); > + if (PageCompound(page)) > + __pagevec_lru_add(pvec); > put_cpu_var(lru_add_pvec); > } That's not _quite_ what I had in mind since that drains the entire pvec every time a large page is encountered. But I'm conflicted about what the right behavior _is_. We'd taking the LRU lock for 'page' anyway, so we might as well drain the pvec. Or, does the additional work to put the page on to a pvec and then immediately drain it overwhelm that advantage? Or does it just not matter? Kirill, do you have a suggestion for how we should be checking for THP pages in code like this? PageCompound() will surely _work_ for anon-THP and your file-THP, but is it the best way to check? > Do we have any tests that I could use to measure performance impact > of such changes before I start to tweak it up? Or maybe it doesn't make > sense at all ? You probably want to very carefully calculate the time to fault a page, then separately to free a page. If we can't manage to detect a delta on a little microbenchmark like that then we'll probably never see one in practice. You'll want to measure the fault time for a 4k pages, 2M pages, and then possibly a mix. You'll want to do this in a highly parallel test to make sure any additional LRU lock overhead shows up. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2016-05-06 16:04 UTC|newest] Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-04-27 17:01 mm: pages are not freed from lru_add_pvecs after process termination Odzioba, Lukasz 2016-04-27 17:01 ` Odzioba, Lukasz 2016-04-27 17:11 ` Dave Hansen 2016-04-27 17:11 ` Dave Hansen 2016-04-28 14:37 ` Michal Hocko 2016-04-28 14:37 ` Michal Hocko 2016-05-02 13:00 ` Michal Hocko 2016-05-02 13:00 ` Michal Hocko 2016-05-04 19:41 ` Odzioba, Lukasz 2016-05-04 19:41 ` Odzioba, Lukasz 2016-05-04 20:16 ` Dave Hansen 2016-05-04 20:16 ` Dave Hansen 2016-05-04 20:36 ` Michal Hocko 2016-05-04 20:36 ` Michal Hocko 2016-05-05 7:21 ` Michal Hocko 2016-05-05 7:21 ` Michal Hocko 2016-05-05 17:25 ` Odzioba, Lukasz 2016-05-05 17:25 ` Odzioba, Lukasz 2016-05-11 7:38 ` Michal Hocko 2016-05-11 7:38 ` Michal Hocko 2016-05-06 15:10 ` Odzioba, Lukasz 2016-05-06 15:10 ` Odzioba, Lukasz 2016-05-06 16:04 ` Dave Hansen [this message] 2016-05-06 16:04 ` Dave Hansen 2016-05-11 7:53 ` Michal Hocko 2016-05-11 7:53 ` Michal Hocko 2016-05-13 11:29 ` Vlastimil Babka 2016-05-13 11:29 ` Vlastimil Babka 2016-05-13 12:05 ` Odzioba, Lukasz 2016-05-13 12:05 ` Odzioba, Lukasz 2016-06-07 9:02 ` Odzioba, Lukasz 2016-06-07 9:02 ` Odzioba, Lukasz 2016-06-07 11:19 ` Michal Hocko 2016-06-07 11:19 ` Michal Hocko 2016-06-08 8:51 ` Odzioba, Lukasz 2016-06-08 8:51 ` Odzioba, Lukasz 2016-05-02 14:39 ` Vlastimil Babka 2016-05-02 14:39 ` Vlastimil Babka 2016-05-02 15:01 ` Kirill A. Shutemov 2016-05-02 15:01 ` Kirill A. Shutemov 2016-05-02 15:13 ` Vlastimil Babka 2016-05-02 15:13 ` Vlastimil Babka 2016-05-02 15:49 ` Dave Hansen 2016-05-02 15:49 ` Dave Hansen 2016-05-02 16:02 ` Kirill A. Shutemov 2016-05-02 16:02 ` Kirill A. Shutemov 2016-05-03 7:37 ` Michal Hocko 2016-05-03 7:37 ` Michal Hocko 2016-05-03 10:07 ` Kirill A. Shutemov 2016-05-03 10:07 ` Kirill A. Shutemov
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