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b=Yy+7bd7wWK11Akz64zjyb9ETsTQsEDXkuUsN6tcHwpwvYCMhDbHlrqwp1+bwrkKYq 9KSylJf5mnx+Y4V7oJ6C1tWzsOeTt89DV14ERJ7HehMvWf1x9Hng4jYsiYa8Ti9UjY ZIuD5GfqcJBgqy+od90T0l2BwSc530EHDZvnfe5KIUvZHtpWX6tGecSYSTFAY9iszE tIq+nduxxxT2Kq9hdisGg+S0BiSc6rAxsoIEsEj+VXmjcQqaFdKYpdH4tD9dwm1dLP B/C1OAjBp+zksOnIFZBdV15EVBVXr/mqBKhCnemobrsyKy4TW5jNjyqxujKxUdJie9 PZCbkX4fvk4ag== Message-ID: <93e9c643-f6fb-4377-ac5a-d91e203ad1a6@kernel.org> Date: Mon, 22 Jun 2026 13:45:38 +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> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 88BF4160003 X-Rspam-User: X-Rspamd-Server: rspam09 X-Stat-Signature: 86hrbk7fyj58ymoaniq9tjp9pdc6w4bz X-HE-Tag: 1782128743-849214 X-HE-Meta: U2FsdGVkX1+eavRze3//Lf1AYeEhTchhmGvWvqOf3gVu5BUj5HjciQtEP6QoQBYWaGk4XmNUgxkVGzTEK9qfEoxNo/F/y3Z/l+LELaWfGf6Uf/6fvJO9ztCJ1KkR8pqIPXDgSSeq+V8wnp5A3EjtnEOJNeXSetbMF9lWCCZ6FfWAKff3eRWDoFAIgh0XF+7mSK1imxoe27EqGSzSg763VBeu2aoXe1vOqb4KH061zLcF5wT+jqsIJ3T50OQFbHVi0JMovNvw0e9GrCwCkKaSnIVAMbBKBUTRsM0L7rJPOMFwAyZ2Z17yOsKbqrIUGTJ53aHE656gRp12YlG3LbQqv+liut79j9Z4VoybF7HiMeUrBS76+oWTX3ZyLPQXAoe0HKnojLqcNUY9gNeA/FdGnp3mTHAceo5rWnub0f7o3xw/9EkYnwnmEELh3cP5zoUbRNJGF1khlXopFSZ5IY/TXUZufci8PTDdqqmVHFVOU2kehXh6BP7j9mcWN5oBisH2IqLy1tsguge4j4z4VDNop15+K1jMy/qdoJXTPgxF5e98awGCMjAXjqCeif+cgjCmvlOCrg9v5jRep1eQjvyfBfdDiUkmS/A+MLQKYAVvrT9dJF87iwrcnkUdbCXGiKnpyrOi/9XRa9KTz7JDKfTinND8EEXGYeSFpjpZgzRKeLPsiPnAZNUBc4cgf/lD7KUbJB8X6YUoY20+DmNN2W6UWcIp+SLOCL6V4B1/YCRfy/yb4WyfP9vmFwRayXQToWj0HOOuJNFbC5MWCCyj/BjfTR4vLQdihNpUprrkHU/vcMCh74PX1+6EI/NH56t9stfU4Wn4GHIWcbexeuRWm9fpta+QUv2eJoy2kpUt1Y0sxtKFbgxvji9LnM+vJD/MgDEUeFuaMHoBtjWgkB4/XgNdZCW7QohhBlr3OV9xYcOurE3xqeQ489VAtZD1Q8yQlUQrW83ZSJrvRcNj1PPQWsD AXnTEu6H 39X2WaPsFSAtICTYTKeW8Dk7ct2dAFNI99+tco+uV2fEUeBewX/7P0D/i19azCSqQsBePxfmx4KtWqvzx/7x3NxvVYYEpZfPE/4vYMP0VlEo3QhnWsF2CZCQ+GNnHGJ813C24iwmx9IU7HMve8S4rYJluIugxnrkMuRwDFSFoiR84beysS0JC3UrMLB0hfXrIolFTHuWDa/6x6MpZP+7RP4/ZoD0lLLO6WomRg1zViH/fHdiJBhbe6VpZj3FhUM9HUPlDvzuy9K+m9FAGOkbLFSz35JnE3vWD2rgar6yKqOjTE24/ZsHwz+ED05k0GmTT5w4RYppfTLaJGUQ= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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) -- Cheers, David