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Thu, 16 Apr 2020 17:38:41 -0700 (PDT) Received: from google.com ([2601:647:4001:3000::50e3]) by smtp.gmail.com with ESMTPSA id gv7sm382543pjb.16.2020.04.16.17.38.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Apr 2020 17:38:39 -0700 (PDT) Date: Thu, 16 Apr 2020 17:38:37 -0700 From: Minchan Kim To: Jaewon Kim , Johannes Weiner Cc: mgorman@suse.de, m.szyprowski@samsung.com, mina86@mina86.com, riel@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, jaewon31.kim@gmail.com, ytk.lee@samsung.com Subject: Re: [PATCH] mm/vmscan: skip layzfree page on reclaim_clean_pages_from_list Message-ID: <20200417003837.GA90471@google.com> References: <20200416033514.6366-1-jaewon31.kim@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200416033514.6366-1-jaewon31.kim@samsung.com> 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: Hi Jaewon, On Thu, Apr 16, 2020 at 12:35:14PM +0900, Jaewon Kim wrote: > This patch fix nr_isolate_* mismatch problem between cma and dirty > lazyfree page. > > If try_to_unmap_one is used for reclaim and it detects a dirty lazyfree > page, then the lazyfree page is changed to a normal anon page having > SwapBacked by commit 18863d3a3f59 ("mm: remove SWAP_DIRTY in ttu"). Even > with the change, reclaim context correctly counts isolated files because > it uses is_file_lru to distinguish file. And the change to anon is not > happened if try_to_unmap_one is used for migration. So migration context > like compaction also correctly counts isolated files even though it uses > page_is_file_lru insted of is_file_lru. Recently page_is_file_cache was > renamed to page_is_file_lru by commit 9de4f22a60f7 ("mm: code cleanup for > MADV_FREE"). > > But the nr_isolate_* mismatch problem happens on cma alloc. There is > reclaim_clean_pages_from_list which is being used only by cma. It was > introduced by commit 02c6de8d757c ("mm: cma: discard clean pages during > contiguous allocation instead of migration") to reclaim clean file pages > without migration. The cma alloc uses both reclaim_clean_pages_from_list > and migrate_pages, and it uses page_is_file_lru to count isolated > files. If there are dirty lazyfree pages allocated from cma memory > region, the pages are counted as isolated file at the beginging but are > counted as isolated anon after finished. > > Mem-Info: > Node 0 active_anon:3045904kB inactive_anon:611448kB active_file:14892kB inactive_file:205636kB unevictable:10416kB isolated(anon):0kB isolated(file):37664kB mapped:630216kB dirty:384kB writeback:0kB shmem:42576kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no > > Like log above, there was too much isolated file, 37664kB, which > triggers too_many_isolated in reclaim when there is no isolated file in > system wide. It could be reproducible by running two programs, doing > MADV_FREE, writing and doing cma alloc, respectively. Although isolated > anon is 0, I found that the internal value of isolated anon was the > negative value of isolated file. > > Fix this by skipping anon pages on reclaim_clean_pages_from_list. The > lazyfree page can be checked by both PageAnon(page) and > page_is_file_lru. But in this case, PageAnon is enough to skip all > anon pages. > > Reported-by: Yong-Taek Lee > Signed-off-by: Jaewon Kim Thanks for the investigation! The thing is MADV_FREEed page since supporting swapless could change his LRU status between reclaim. I am worry about voiding the optimization we have kept in CMA but also don't have good idea, either so I tend to agree with this. Let me Cc Johannes who might have better idea. > --- > mm/vmscan.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index b06868fc4926..9380a18eef5e 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1497,6 +1497,9 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone, > LIST_HEAD(clean_pages); > > list_for_each_entry_safe(page, next, page_list, lru) { > + /* to avoid race with MADV_FREE anon page */ > + if (PageAnon(page)) > + continue; > if (page_is_file_lru(page) && !PageDirty(page) && > !__PageMovable(page) && !PageUnevictable(page)) { > ClearPageActive(page); > -- > 2.13.7 >