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Thu, 18 Dec 2025 03:31:50 +0000 (UTC) Date: Thu, 18 Dec 2025 11:31:46 +0800 From: Baoquan He To: Kairui Song Cc: linux-mm@kvack.org, Andrew Morton , Barry Song , Chris Li , Nhat Pham , Yosry Ahmed , David Hildenbrand , Johannes Weiner , Youngjun Park , Hugh Dickins , Baolin Wang , Ying Huang , Kemeng Shi , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" , linux-kernel@vger.kernel.org, Kairui Song Subject: Re: [PATCH v4 12/19] mm, swap: use swap cache as the swap in synchronize layer Message-ID: References: <20251205-swap-table-p2-v4-0-cb7e28a26a40@tencent.com> <20251205-swap-table-p2-v4-12-cb7e28a26a40@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251205-swap-table-p2-v4-12-cb7e28a26a40@tencent.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: B5EE2C0010 X-Stat-Signature: mmh98kxqz1h3wch4nru86dsc8q9rjrzp X-HE-Tag: 1766028722-878921 X-HE-Meta: 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 ize9Ectv Bdl5JLBiZgXkzGXa0qZB3adYRuvYCOsZ+qbcjy2q51ndCCCvnIMp7iF7Vsei1upg6Q5b6eSCpzqAT0kM2Joh2Rovdz18CWppY5bZnqY43GvXVYQA= 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 12/05/25 at 03:29am, Kairui Song wrote: > From: Kairui Song > > Current swap in synchronization mostly uses the swap_map's > SWAP_HAS_CACHE bit. Whoever sets the bit first does the actual > work to swap in a folio. > > This has been causing many issues as it's just a poor implementation > of a bit lock. Raced users have no idea what is pinning a slot, so > it has to loop with a schedule_timeout_uninterruptible(1), which is > ugly and causes long-tailing or other performance issues. Besides, > the abuse of SWAP_HAS_CACHE has been causing many other troubles for > synchronization or maintenance. > > This is the first step to remove this bit completely. > > We have just removed all swap in paths that bypass the swap cache, and I think we didn't remove swap in paths that bypss the swap cache, we just add folio to swap cache in those swap in paths where swap cache is bypassed.