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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1u8Olx-0000000FMFm-1xJm; Fri, 25 Apr 2025 19:31:41 +0000 Date: Fri, 25 Apr 2025 20:31:41 +0100 From: Matthew Wilcox To: John Reiser Cc: linux-mm@kvack.org Subject: Re: msync() seems not to clean the data cache Message-ID: References: <9a70a70d-9dce-46a0-997e-b8a346e60902@bitwagon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9a70a70d-9dce-46a0-997e-b8a346e60902@bitwagon.com> X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: A497D80010 X-Stat-Signature: zxhwf7bn1rfehfxq65ijjr6yxh3h6mz8 X-Rspam-User: X-HE-Tag: 1745609503-934465 X-HE-Meta: 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 snlGv5eW ZU0F+7S9Rh+nPdVuic8D+lZ7ZrpYNJZaug+FKQt1t7xVs/mtMoXpU/HJXl4sKxmjDMofa6aw4Ha2L5PdCBwouqSnVwRz4MRBZ2eBwtkbc1g5IGmO+Ajdn1Ntf5iZ/H/dGuAqaFYGmgbxZbrPZc371kWZoXKyBra0/VUubJXi5amzKDZlUOZ4TEp4S6EfIGccbQnDkUY8PQDPjdtWkgk/uDTxX1uN4ehVrP7fc 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 Fri, Apr 25, 2025 at 12:17:37PM -0700, John Reiser wrote: > The system call write() cleans the hardware data cache (writes any dirty > values from the data cache into RAM memory) before passing to the VFS > the region to be written. The system call msync() should do likewise. > Currently msync() does not clean the hardware data cache, as seen on > PowerPC, PowerPC64, and arm64; and probably any CPU that does not > have a Write-through cache. (x86 and x86_64 do have write-through.) I think you're right; we don't flush before writeback. Does this fix your problem? +++ b/mm/page-writeback.c @@ -2432,6 +2432,7 @@ static bool folio_prepare_writeback(struct address_space *mapping, if (!folio_clear_dirty_for_io(folio)) return false; + flush_dcache_folio(folio); return true; } By the way, x86 does not have writethrough caches. Instead it has DMA coherent caches, so modified cachelines in the cache will take precedence over the contents of memory.