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Thu, 11 Apr 2024 11:23:45 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id TeMtBkHIF2bkBQAAD6G6ig (envelope-from ); Thu, 11 Apr 2024 11:23:45 +0000 Date: Thu, 11 Apr 2024 13:23:43 +0200 From: Oscar Salvador To: Miaohe Lin Cc: Matthew Wilcox , Jane Chu , linux-mm@kvack.org Subject: Re: [PATCH v2 07/11] mm/memory-failure: Convert memory_failure() to use a folio Message-ID: References: <20240408194232.118537-1-willy@infradead.org> <20240408194232.118537-8-willy@infradead.org> <2cc02f91-fbca-4160-9f31-bfb54f882f08@oracle.com> <1677b7a8-179d-4e4f-a7f3-5d6244586cdb@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 1489716000A X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 54ojwwkp1yqzhjdgfhprp673js8od3e1 X-HE-Tag: 1712834627-11405 X-HE-Meta: U2FsdGVkX198cIgJ67jzqZIM5IoA/NM+U2ZBHtpX8dWseuhNc7OqfA23B6HErJ2yiLF8jBL1Uto330QdsXkygxCESlfUqP3G51vszWtZ5Hk1VxpPlzTBQpt1UgHNnHkdGcZfKa53elUT8KFXV+XWWayXFsk71OEgsGxwDYbzlnO4zmZXcdqG+lbbUZsZTL0Xw4dyB0mVPebtqtYQzGvPnNrVxIc/zTV2XZUbUJqAJnTUCztRYB0UuDz7llHf2l8dZjsNapKyHqoU3lzsTmJnmPvy+qstxTJCCH0pEylNHgxYYVlwO1li3LmRngrSLv9JQTdWN7FVb49Yka8F5mXSvgOzXK9T5u7Okb2pnK9OPiy0J3t8+bAPbQ+KPYo/Cht40Wcx8RJd0ZLisBeCsSF2gFJcFkRb/KW4CfAbhN4xyflLaTCsqvyOK5yzesdT+FU0VGYqP/iEjzH5g9bia6hMSEQMKm4HJV5XNB+xCf9pvdlgwMOhr89KecB1HbQqc9Pq+XSR1tTYVQCLrYXtbUPaCZQ1Guggta7MQx4f7nFfzzClyPoDWuIhj0FsPdbGB9/yKR8YYs9MrG4xOfG7UlO6uHa9p3NrJMMuD78vFosJmidLQwHUpbVRYZry+gZYw/l+CuJNFYsgGpKi5NmEpR1LH9aTQSyWeJEwEVBlKG6YfP6qmMGwNgGRzr8ndQAKHzLQ+20AOcRBDxd671YfaFqR5G72J13NAqh++lTy5X3VpOhdi8w/9HXYJ7E1eX2rX+Euuv599magAfdcZHuBygXr9rdYhCyjHPAixo0ClQdU1wsDyastlsmQkd4m/qw35RzWXVBAMnPUqlC/26xpsFqquKPm/s+WRczwl/B5skr97q4FPzR4eB67xwUo/zyqGoQ7O+bNE0u8z8sXTFacoBPPzFNctpxcks/vQcujRi6snR/m03XGeXMc0hLeRl1DOtlTRfcJA1o3mPMdUOE3Su8 2mzNy3Yh WQOJyQm9NzNy0iB+iXSfHA3TadUDsKotEWwYV0EGkgOIvvOd3M58C1u8fTJBPIrGosZA/YdBFVvUqjAjpXXAefPESYoj+v48FMIUxL6f9M+3uSGbxHWRQ8leeunjDoerm3oBJjn0KiHOfC12adih0BWzQf0zmI92CuqVakofm2KOfoUxOkg3oeT1YiZ6VSt8QcgCJYlmkRT/QLDVZ8HCJy724Vv3XC4V5k268oATpo7RaleTPtJ+V9xKhhSIIUaOsSCrc 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 Thu, Apr 11, 2024 at 05:00:33PM +0800, Miaohe Lin wrote: > But as code changes, the above page lock shift is gone. And I think below logic can't > trigger now. As we hold extra page refcnt so page can't be coallesced into a new THP or Slab page. So I was wrong. I did not check the slap part, but I did check the code that tries to coallesce pages. We have the following check in hpage_collapse_scan_pmd(): /* * * Here the check may be racy: * it may see total_mapcount > refcount in some cases? * But such case is ephemeral we could always retry collapse * later. However it may report false positive if the page * has excessive GUP pins (i.e. 512). Anyway the same check * will be done again later the risk seems low. */ if (!is_refcount_suitable(folio)) { result = SCAN_PAGE_COUNT; goto out_unmap; } So I guess that since we hold an extra refcount from memory-failure code, this page cannot be part of a THP anymore. If we confirm that the same goes for slab, I would replace that with your warn check. In this way, if we ever trigger that warn path, as least we will know that that possibility exists. So it is a good way to get rid of false assumptions and code burden. -- Oscar Salvador SUSE Labs