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t=1782129663; bh=Hb+xK1K2v16uboBzyh3TzN4n8wpgYjwMIIEfcewwUJg=; h=Date:Subject:From:To:Cc:References:In-Reply-To; b=fp5uGzNY7paUzv00kCFpF+NxNCdwOOIxnW9qL4vct2NCpHuFSbM4tyq5o7aFNuUQx 3zM0af3z5joZrCn43s/96UJEyoSljgjaBMixwLm80KN2an3jg6+yLy/1grrDAxpCSu Y5d0FiaMiFc824QPjb7SAIXhSFLzUTrVoN5WvBTGSjbYeFtoo5iWBqJfGc1/OvSBJU Tt8v/3aA8QRU9dwStjFgV9Y0rciWhcf19Rzn7vQcHTw2MJR7C6gj6Eb+1LFaMSW0w5 QGR4uId+6WhxK9cT4M/OBKlNslhd/mAevTq6qAk69nIIjtQ3q0HEpWnVKl1qAZLAXP jFiHPDTzlQ7Jw== Message-ID: Date: Mon, 22 Jun 2026 14:00:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fs/proc: fix KPF_KSM reported for all anonymous pages From: "David Hildenbrand (Arm)" To: Jinjiang Tu , akpm@linux-foundation.org, ziy@nvidia.com, luizcap@redhat.com, willy@infradead.org, linmiaohe@huawei.com, svetly.todorov@memverge.com, xu.xin16@zte.com.cn, chengming.zhou@linux.dev, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Cc: wangkefeng.wang@huawei.com, sunnanyong@huawei.com References: <20260622091539.836531-1-tujinjiang@huawei.com> <93e9c643-f6fb-4377-ac5a-d91e203ad1a6@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 04AB0100015 X-Stat-Signature: 3gcq8mta3r6bxt6akn14ki8ksyraai1d X-HE-Tag: 1782129663-480587 X-HE-Meta: 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 RuEGoenN l/k+MzYJrf7Yref3QPbeK8VQbFx/cMuV6waRCinINkTy+8ctYywJfeHDRRg5f8ImbGnZ37NEQiKgDx6xyoo7NeEYlkjuv+mDjLf7H5pD/hUsLAyZ/SLxzcuOyI0ynqa+3E9fLH8NWJIBFwYrlfqEpSd0GlBNqbTvzHyTYSGAR55cEXGdX+QzNt3kE/zsPUi5jYX0z6BrCoorARxXBGt3MD4Un21iJU1J2TqKKEp9GBmw4Wi2PBtDRjiUDhRnuSldAV69fFb30CC4IOIYwE7WNOlJ8lKANJC6+54bmziI5g1ZrEudeN31ijwsoRZC7TV3W3p0GSSOacH/lxB0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/22/26 13:45, David Hildenbrand (Arm) wrote: > On 6/22/26 11:15, Jinjiang Tu wrote: >> Reading /proc/kpageflags for any anonymous page returns KPF_KSM set, even >> when KSM is not in use. As a result, tools misclassify all anonymous pages >> as KSM merged. >> >> In stable_page_flags(), if the page is anonymous, then use (mapping & >> FOLIO_MAPPING_KSM) check to identify if the anonymous page is KSM page. >> However, FOLIO_MAPPING_KSM is FOLIO_MAPPING_ANON | FOLIO_MAPPING_ANON_KSM, >> (mapping & FOLIO_MAPPING_KSM) check returns true for all nonymous pages. >> >> To fix it, use FOLIO_MAPPING_ANON_KSM instead. >> >> Fixes: dee3d0bef2b0 ("proc: rewrite stable_page_flags()") > > Right, > > #define PAGE_MAPPING_KSM (PAGE_MAPPING_ANON | PAGE_MAPPING_ANON_KSM) > > Which we later renamed to FOLIO_MAPPING_KSM. > > > Before switching to manual flag checks, PageKsm() translated to folio_test_ksm() > that checked whether the values actually matched: > > ((unsigned long)folio->mapping & PAGE_MAPPING_FLAGS) == PAGE_MAPPING_KSM; > > > This only affects /proc/kpageflags (well, and hwpoison inject on a weird testing > interface), so it's not really that relevant for real workloads (debugging and > testing). > > So not sure whether we should CC:stable. Likely not. > >> Signed-off-by: Jinjiang Tu >> --- >> fs/proc/page.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/proc/page.c b/fs/proc/page.c >> index f9b2c2c906cd..cef8ded97610 100644 >> --- a/fs/proc/page.c >> +++ b/fs/proc/page.c >> @@ -173,7 +173,7 @@ u64 stable_page_flags(const struct page *page) >> u |= 1 << KPF_MMAP; >> if (is_anon) { >> u |= 1 << KPF_ANON; >> - if (mapping & FOLIO_MAPPING_KSM) >> + if (mapping & FOLIO_MAPPING_ANON_KSM) > > > Wonder whether we should just do > > if ((mapping & FOLIO_MAPPING_FLAGS) == FOLIO_MAPPING_KSM) > > To match what we have in folio_test_ksm. > > (although I doubt we would reuse this flag for other purposes, likely > it's more future proof to check it like that) > And just to mention: given that this function now operates on folio+page snapshot now, I think we could even stop doing this manual folio->mapping dance here and just use folio_test_anon() + folio_test_ksm(), as the values cannot change concurrently. But that should rather be a separate cleanup (and needs double-checking). -- Cheers, David