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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tUeOf-0000000Fd0k-2gMk; Mon, 06 Jan 2025 04:07:21 +0000 Date: Mon, 6 Jan 2025 04:07:21 +0000 From: Matthew Wilcox To: Baolin Wang Cc: akpm@linux-foundation.org, hughd@google.com, david@redhat.com, wangkefeng.wang@huawei.com, kasong@tencent.com, ying.huang@linux.alibaba.com, 21cnbao@gmail.com, ryan.roberts@arm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm: shmem: skip swapcache for swapin of synchronous swap device Message-ID: References: <04997e54c276eff40a6119a90d36a4e71aade89c.1735806921.git.baolin.wang@linux.alibaba.com> <8344980d-4c22-4694-9a76-2e5a7ada50cb@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8344980d-4c22-4694-9a76-2e5a7ada50cb@linux.alibaba.com> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: C918EC000A X-Stat-Signature: pgh5d7hrssnwnx5jjt8ezac6wj3r1mew X-Rspam-User: X-HE-Tag: 1736136461-560026 X-HE-Meta: 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 mncCrHUd 8i+kRtBObsXyvbtIl9bs8kKFH/c3pEy0dwFHaGfPutgrWSmotuEfXvsOwhXUEzojjPVi82chPR95kewge460YR4cztEBbYl0pPbyuvjUct1RpcT5xvGwAnH0U3HbHnsX5Vrwh1lGJ29ko1fNY+uKSSOL5wRo1VB+8wAKVZuiF/iM1snmSZ3k/SRk3DXuDd5pa03rOvSseXYYdhgWvQ0dWSERIzjc33s6j4RWOer0icX1j++E= 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, Jan 06, 2025 at 11:46:04AM +0800, Baolin Wang wrote: > On 2025/1/2 21:10, Matthew Wilcox wrote: > > On Thu, Jan 02, 2025 at 04:40:17PM +0800, Baolin Wang wrote: > > > With fast swap devices (such as zram), swapin latency is crucial to applications. > > > For shmem swapin, similar to anonymous memory swapin, we can skip the swapcache > > > operation to improve swapin latency. > > > > OK, but now we have more complexity. Why can't we always skip the > > swapcache on swapin? > > Skipping swapcache is used to swap-in shmem large folios, avoiding the large > folios being split. Meanwhile, since the IO latency of syncing swap devices > is relatively small, it won't cause the IO latency amplification issue. > > But for async swap devices, if we swap-in the large folio one-time, I am > afraid the IO latency can be amplified. And I remember we still haven't > reached an agreement here[1], so let's step by step and start with the sync > swap devices first. Regardless of whether we choose to swap-in an order-0 or a large folio, my point is that we should always do it to the pagecache rather than the swap cache.