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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1sEB3R-0000000EEkG-1cMp; Mon, 03 Jun 2024 17:01:05 +0000 Date: Mon, 3 Jun 2024 18:01:05 +0100 From: Matthew Wilcox To: Dave Hansen Cc: David Hildenbrand , Byungchul Park , Byungchul Park , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, akpm@linux-foundation.org, ying.huang@intel.com, vernhao@tencent.com, mgorman@techsingularity.net, hughd@google.com, peterz@infradead.org, luto@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, rjgolo@gmail.com Subject: Re: [PATCH v11 09/12] mm: implement LUF(Lazy Unmap Flush) defering tlb flush when folios get unmapped Message-ID: References: <20240531092001.30428-1-byungchul@sk.com> <20240531092001.30428-10-byungchul@sk.com> <26dc4594-430b-483c-a26c-7e68bade74b0@redhat.com> <20240603093505.GA12549@system.software.com> <35866f91-7d96-462a-aa0a-ac8a6b8cbcf8@redhat.com> <196481bb-b86d-4959-b69b-21fda4daae77@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <196481bb-b86d-4959-b69b-21fda4daae77@intel.com> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: DAA6440019 X-Rspam-User: X-Stat-Signature: kf57u55xz67zmm63cixtc1iunshcxcwa X-HE-Tag: 1717434084-772999 X-HE-Meta: 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 3NWLaxzu lp9NgDBO87wte0X1YCQkwEvN9q5bCVTLiCkJYgDVFoaZcdwyU1qeDYmrdPQLd05qt6mbote+CRRG3eENpMhv7F9JbJDJ992MAobtiWEix6SR53CRcZmxtbQEkS0N2AEKp+FP+tVfS2j115ggRXG+fX10sAP2VUuM3+vwXLKYvwj41S+0yZufWRWFX20NNdasUI7yYGLSr86tsht5HRIo9LL9Ogw== 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 Mon, Jun 03, 2024 at 09:37:46AM -0700, Dave Hansen wrote: > Yeah, we'd need some equivalent of a PTE marker, but for the page cache. > Presumably some xa_value() that means a reader has to go do a > luf_flush() before going any farther. I can allocate one for that. We've got something like 1000 currently unused values which can't be mistaken for anything else. > That would actually have a chance at fixing two issues: One where a new > page cache insertion is attempted. The other where someone goes to look > in the page cache and takes some action _because_ it is empty (I think > NFS is doing some of this for file locks). > > LUF is also pretty fundamentally built on the idea that files can't > change without LUF being aware. That model seems to work decently for > normal old filesystems on normal old local block devices. I'm worried > about NFS, and I don't know how seriously folks take FUSE, but it > obviously can't work well for FUSE. I'm more concerned with: - page goes back to buddy - page is allocated to slab - application reads through stale TLB entry and sees kernel memory Or did that scenario get resolved?