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Fri, 17 Apr 2020 08:14:01 -0700 (PDT) Received: from google.com ([2601:647:4001:3000::50e3]) by smtp.gmail.com with ESMTPSA id a17sm7688794pfr.24.2020.04.17.08.13.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Apr 2020 08:14:00 -0700 (PDT) Date: Fri, 17 Apr 2020 08:13:58 -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: <20200417151358.GA178621@google.com> References: <20200416033514.6366-1-jaewon31.kim@samsung.com> <20200417003837.GA90471@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200417003837.GA90471@google.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: On Thu, Apr 16, 2020 at 05:38:37PM -0700, Minchan Kim wrote: > 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 > > Hi Jaewon, How about this idea? I think it could solve the issue with keeping CMA alloc latency optimization. diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h index 292485f3d24d..10cc932e209a 100644 --- a/include/linux/vmstat.h +++ b/include/linux/vmstat.h @@ -29,6 +29,7 @@ struct reclaim_stat { unsigned nr_activate[2]; unsigned nr_ref_keep; unsigned nr_unmap_fail; + unsigned nr_lazyfree_fail; }; enum writeback_stat_item { diff --git a/mm/vmscan.c b/mm/vmscan.c index 4c8a1cdccbba..b390f6094f2f 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1296,11 +1296,15 @@ static unsigned long shrink_page_list(struct list_head *page_list, */ if (page_mapped(page)) { enum ttu_flags flags = ttu_flags | TTU_BATCH_FLUSH; + bool lazyfree = PageAnon(page) && !PageSwapBacked(page); if (unlikely(PageTransHuge(page))) flags |= TTU_SPLIT_HUGE_PMD; + if (!try_to_unmap(page, flags)) { stat->nr_unmap_fail += nr_pages; + if (lazyfree && PageSwapBacked(page)) + stat->nr_lazyfree_fail += nr_pages; goto activate_locked; } } @@ -1492,8 +1496,8 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone, .priority = DEF_PRIORITY, .may_unmap = 1, }; - struct reclaim_stat dummy_stat; - unsigned long ret; + struct reclaim_stat stat; + unsigned long reclaimed; struct page *page, *next; LIST_HEAD(clean_pages); @@ -1505,11 +1509,21 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone, } } - ret = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc, - TTU_IGNORE_ACCESS, &dummy_stat, true); + reclaimed = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc, + TTU_IGNORE_ACCESS, &stat, true); list_splice(&clean_pages, page_list); - mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -ret); - return ret; + mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -reclaimed); + /* + * Since lazyfree pages are isolated from file LRU from the beginning, + * they will rotate back to anonymous LRU in the end if it failed to + * discard so isolated count will be mismatched. + * Compensate the isolated count for both LRU lists. + */ + mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_ANON, + stat->nr_lazyfree_fail); + mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, + -stat->nr_lazyfree_fail); + return reclaimed; } /* -- 2.26.1.301.g55bc3eb7cb9-goog