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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id az33-20020a05620a172100b00648af7287desm2799830qkb.26.2022.03.04.13.25.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Mar 2022 13:25:20 -0800 (PST) Date: Fri, 4 Mar 2022 13:25:18 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@ripple.anvils To: Andrew Morton cc: David Hildenbrand , Hugh Dickins , Matthew Wilcox , Nicholas Piggin , Yu Zhao , Yang Shi , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH mmotm v2] mm: delete __ClearPageWaiters() In-Reply-To: <6e5262ff-8596-a86-7388-eddb2b2c53c@google.com> Message-ID: <3eafa969-5b1a-accf-88fe-318784c791a@google.com> References: <351df0af-78f2-c20-2a6d-e5f978e5ca1@google.com> <9dda55d5-eafa-3177-2a4c-32ccb7e146e3@google.com> <90aafe84-fe7d-c70e-8e15-c222869f30fc@redhat.com> <6e5262ff-8596-a86-7388-eddb2b2c53c@google.com> MIME-Version: 1.0 X-Rspamd-Queue-Id: 1643716000E X-Stat-Signature: 81sjy7hsnbpqqah1ye5cz4wigpp9q1zf X-Rspam-User: Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=rIWW6nrq; spf=pass (imf08.hostedemail.com: domain of hughd@google.com designates 209.85.219.43 as permitted sender) smtp.mailfrom=hughd@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam07 X-HE-Tag: 1646429121-95583 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: The PG_waiters bit is not included in PAGE_FLAGS_CHECK_AT_FREE, and vmscan.c's free_unref_page_list() callers rely on that not to generate bad_page() alerts. So __page_cache_release(), put_pages_list() and release_pages() (and presumably copy-and-pasted free_zone_device_page()) are redundant and misleading to make a special point of clearing it (as the "__" implies, it could only safely be used on the freeing path). Delete __ClearPageWaiters(). Remark on this in one of the "possible" comments in folio_wake_bit(), and delete the superfluous comments. Signed-off-by: Hugh Dickins Tested-by: Yu Zhao Reviewed-by: David Hildenbrand Reviewed-by: Yang Shi --- v2: Add Tested-by from Yu Zhao. Update to latest function names in the commit message. Reword comment in folio_wake_bit() per David Hildenbrand. include/linux/page-flags.h | 2 +- mm/filemap.c | 23 ++++++++--------------- mm/memremap.c | 2 -- mm/swap.c | 4 ---- 4 files changed, 9 insertions(+), 22 deletions(-) --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -481,7 +481,7 @@ static unsigned long *folio_flags(struct folio *folio, unsigned n) TESTSETFLAG_FALSE(uname, lname) TESTCLEARFLAG_FALSE(uname, lname) __PAGEFLAG(Locked, locked, PF_NO_TAIL) -PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) __CLEARPAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) +PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) PAGEFLAG(Error, error, PF_NO_TAIL) TESTCLEARFLAG(Error, error, PF_NO_TAIL) PAGEFLAG(Referenced, referenced, PF_HEAD) TESTCLEARFLAG(Referenced, referenced, PF_HEAD) --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1179,24 +1179,17 @@ static void folio_wake_bit(struct folio *folio, int bit_nr) } /* - * It is possible for other pages to have collided on the waitqueue - * hash, so in that case check for a page match. That prevents a long- - * term waiter + * It's possible to miss clearing waiters here, when we woke our page + * waiters, but the hashed waitqueue has waiters for other pages on it. + * That's okay, it's a rare case. The next waker will clear it. * - * It is still possible to miss a case here, when we woke page waiters - * and removed them from the waitqueue, but there are still other - * page waiters. + * Note that, depending on the page pool (buddy, hugetlb, ZONE_DEVICE, + * other), the flag may be cleared in the course of freeing the page; + * but that is not required for correctness. */ - if (!waitqueue_active(q) || !key.page_match) { + if (!waitqueue_active(q) || !key.page_match) folio_clear_waiters(folio); - /* - * It's possible to miss clearing Waiters here, when we woke - * our page waiters, but the hashed waitqueue has waiters for - * other pages on it. - * - * That's okay, it's a rare case. The next waker will clear it. - */ - } + spin_unlock_irqrestore(&q->lock, flags); } --- a/mm/memremap.c +++ b/mm/memremap.c @@ -487,8 +487,6 @@ void free_zone_device_page(struct page *page) if (WARN_ON_ONCE(!page->pgmap->ops || !page->pgmap->ops->page_free)) return; - __ClearPageWaiters(page); - mem_cgroup_uncharge(page_folio(page)); /* --- a/mm/swap.c +++ b/mm/swap.c @@ -97,7 +97,6 @@ static void __page_cache_release(struct page *page) mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages); count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages); } - __ClearPageWaiters(page); } static void __put_single_page(struct page *page) @@ -152,7 +151,6 @@ void put_pages_list(struct list_head *pages) continue; } /* Cannot be PageLRU because it's passed to us using the lru */ - __ClearPageWaiters(page); } free_unref_page_list(pages); @@ -966,8 +964,6 @@ void release_pages(struct page **pages, int nr) count_vm_event(UNEVICTABLE_PGCLEARED); } - __ClearPageWaiters(page); - list_add(&page->lru, &pages_to_free); } if (lruvec)