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[2003:d8:2f28:4900:2c24:4e20:1f21:9fbd]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8e0d571sm15283730f8f.57.2025.07.15.05.31.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Jul 2025 05:31:46 -0700 (PDT) Message-ID: Date: Tue, 15 Jul 2025 14:31:45 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 mm-new] fs/proc/page: avoid anon folio checks on typed pages except hugetlb To: Harry Yoo , Andrew Morton Cc: Matthew Wilcox , David Rientjes , Christoph Lameter , Roman Gushchin , linux-mm@kvack.org, Vlastimil Babka References: <20250715120748.9290-1-harry.yoo@oracle.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20250715120748.9290-1-harry.yoo@oracle.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: GyIcD5wGaBf3q0lY31QafsGlXFbewOtfD7CGXLL9C_w_1752582707 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: et56qcxk9mtd94pahm6zsksoc4c6t8ky X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 63381160014 X-Rspam-User: X-HE-Tag: 1752582711-722262 X-HE-Meta: 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 IgkncXgv 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 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: List-Subscribe: List-Unsubscribe: On 15.07.25 14:07, Harry Yoo wrote: > folio_test_anon() and folio_test_ksm() may return false positives when > invoked on typed pages (except hugetlb folios), because lower bits of > folio->mapping may be set even when they do not indicate > FOLIO_MAPPING_* flags. > > This leads to tools/mm/page-types reporting pages with > KPF_SLAB, KPF_ANON and KPF_KSM (with flags, page-counts, MB omitted): > $ sudo ./page-types | grep slab > _______S___________________________________ slab > _______S____a________x_____________________ slab,anonymous,ksm > > Currently, and going forward (The New York interpretation), > typed pages except hugetlb do not have FOLIO_MAPPING_* flags. > In the future, they won't even cast to folios. > > For now, avoid checking FOLIO_MAPPING_* flags on pages if they are > typed pages that are not hugetlb folios. > > Update the comment in FOLIO_MAPPING_* flags accordingly. > > Fixes: 130d4df57390 ("mm/sl[au]b: rearrange struct slab fields to allow larger rcu_head") > Suggested-by: Vlastimil Babka > Signed-off-by: Harry Yoo > --- > > v2->v3: Did not introduce folio_has_mapcount() per David's suggestion > v2: https://lore.kernel.org/linux-mm/20250707120740.4413-1-harry.yoo@oracle.com > > fs/proc/page.c | 19 +++++++++++-------- > include/linux/page-flags.h | 15 +++++++++------ > 2 files changed, 20 insertions(+), 14 deletions(-) > > diff --git a/fs/proc/page.c b/fs/proc/page.c > index 0cdc78c0d23f..07582dbdef45 100644 > --- a/fs/proc/page.c > +++ b/fs/proc/page.c > @@ -148,18 +148,21 @@ u64 stable_page_flags(const struct page *page) > folio = page_folio(page); > > k = folio->flags; > - mapping = (unsigned long)folio->mapping; > - is_anon = mapping & FOLIO_MAPPING_ANON; > > /* > * pseudo flags for the well known (anonymous) memory mapped pages > */ > - if (page_mapped(page)) > - u |= 1 << KPF_MMAP; > - if (is_anon) { > - u |= 1 << KPF_ANON; > - if (mapping & FOLIO_MAPPING_KSM) > - u |= 1 << KPF_KSM; > + if (!page_has_type(&folio->page) || folio_test_hugetlb(folio)) { > + mapping = (unsigned long)folio->mapping; > + is_anon = mapping & FOLIO_MAPPING_ANON; > + > + if (page_mapped(page)) > + u |= 1 << KPF_MMAP; Note: Luiz switches to folio_mapped() in his patch that is in mm-new. > + if (is_anon) { > + u |= 1 << KPF_ANON; > + if (mapping & FOLIO_MAPPING_KSM) > + u |= 1 << KPF_KSM; Can we just switch to folio_test_anon() and folio_test_ksm() ? I don't really see a reason to not do that. Willy converted these checks from page -> mapping, but we should really just use the folio_test_* functions I think. And looking at it, I think Willy introduced an issue in: commit dee3d0bef2b00772be430425832ead6aa9d707f9 Author: Matthew Wilcox (Oracle) Date: Tue Mar 26 17:10:32 2024 +0000 proc: rewrite stable_page_flags() We replaced if (PageKsm(page)) essentially by if (mapping & PAGE_MAPPING_KSM) But #define PAGE_MAPPING_KSM (PAGE_MAPPING_ANON | PAGE_MAPPING_ANON_KSM) So wouldn't we just indicate *all* anon pages as ... KSM pages? > + } > } > > /* > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 8e4d6eda8a8d..26ae4c7cf8dd 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -706,12 +706,15 @@ PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted) > * address_space which maps the folio from disk; whereas "folio_mapped" > * refers to user virtual address space into which the folio is mapped. > * > - * For slab pages, since slab reuses the bits in struct page to store its > - * internal states, the folio->mapping does not exist as such, nor do > - * these flags below. So in order to avoid testing non-existent bits, > - * please make sure that folio_test_slab(folio) actually evaluates to > - * false before calling the following functions (e.g., folio_test_anon). > - * See mm/slab.h. > + * For certain typed pages like slabs, since they reuse bits in struct page > + * to store internal states, folio->mapping does not point to a valid > + * mapping, nor do these flags exist. To avoid testing non-existent bits, > + * make sure I would write that explicitly: that you are dealing with an actual folio: either page has no type or the type indicates a folio (hugetlb). -- Cheers, David / dhildenb