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b=jHY6LLi0YYVjV0LQFOa7dphB55vNXkFWVa7dJbfePYtvE4DSO6GpHbbbSJHyuNaAR mqQ4aGqYrpdQ8bv/sg4cQKRF0Jq+vQcgGMnWpbIKrACyjLEbzl5mv/iKiBxHNwN7bU WjG6uOzqxaIMWKAp8VGgviMyul3O2FSMGX1vcTZhkDm+EcDlnfPtocD33lq3zeAxYQ Y5Xmv6gviPpQN0JE2Kvy1uSWucShBwjpR5KmW/BbQSkVai0dT2iKw60g8azTop04XS cuc1CR/fTTdMO6PGkphwFJrhbqZCD3DyjAR+Pf9JkuYhbYEDDv+ZL0XMmGhqmujIDv CnCspcYIkyjow== Message-ID: <6e39171c-8333-463d-9ea6-db331965d2c4@kernel.org> Date: Thu, 25 Jun 2026 08:39:54 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fs/proc: fix KPF_KSM reported for all anonymous pages 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> <601fb5dd-18e1-4a6c-bc99-dc2a655240e2@huawei.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 7056F20003 X-Rspam-User: X-Stat-Signature: 8fqqmb7ypopwu67n7tksebq1s6putrbx X-HE-Tag: 1782369600-441050 X-HE-Meta: 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 EoV44lra d1uA5Mzd6MIl+gRdvRebnuQtCPNcVpLsUZNPWOeqF54oVbmERDDrkPe1IA7G56DZA2GrT1+07EJOrRWi5wl6BOhbdS/xhHdQCWV/yKnI9qqlOkmEeKw4HIiv8HAXJAdultoUx8I229c2OQuR3pGj006geoMuMD28Xv76z4u/wQmOxyW2hwYCFbOULvSQnTZHILXjA9kE8BGIl1HA14UG6AIJTPzPikk28HPjk5E6LttsfCZh7obmgSOFKCaEKIxXMjA0RP6K+/IZpRUD4S16Ao+Cgti0iKVVuvjpzzax4SVk/Uhn1eajwwasgs8usKyIEhfilxKqQoHjHiwhdKwHOuflihSG4O/hiv1cK Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/23/26 03:37, Jinjiang Tu wrote: > > 在 2026/6/22 19:45, David Hildenbrand (Arm) 写道: >> 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. > > /proc/kpageflags is generally used only for analysis and is unlikely to be > used in production environments. I found this issue due to I was analyzing > pfns allocated by which stacks are KSM-merged. So I think it's unnecessary > to CC:stable. > >>> 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) > > Both are ok. The following check has checked FOLIO_MAPPING_ANON, > >     if (is_anon) { >         if (mapping & FOLIO_MAPPING_ANON_KSM) >     } > > So it's equivalent to do >     if ((mapping & FOLIO_MAPPING_FLAGS) == FOLIO_MAPPING_KSM) > or >     if (mapping & FOLIO_MAPPING_ANON_KSM) As I said, matching precisely what we have in folio_test_ksm() is clearer. We don't have any users of FOLIO_MAPPING_ANON_KSM outside of page-flags.h for a reason :) -- Cheers, David