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Mon, 01 Apr 2024 08:20:53 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Nhat Pham Date: Mon, 1 Apr 2024 08:20:40 -0700 Message-ID: Subject: Re: [PATCH] mm: swap: prejudgement swap_has_cache to avoid page allocation To: Kairui Song Cc: Zhaoyu Liu , akpm@linux-foundation.org, ying.huang@intel.com, songmuchun@bytedance.com, david@redhat.com, willy@infradead.org, chrisl@kernel.org, yosryahmed@google.com, guo.ziliang@zte.com.cn, linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: B2165A0011 X-Stat-Signature: 69nk46a6e1bbxsdy4yp83bej7oqgg5kh X-HE-Tag: 1711984854-353656 X-HE-Meta: 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 dK7En3e4 rwB1HqeDxBi8+IVnSi24OHQprZ2Lm8mIZpkDy6jbycXR3NL5rVwPJfIZuDpWpnRiZSPxNc5bL5Y9b05Rm64YpTsqUIheOwljMeOWD8bhtKizkPHJSNs6f1P9C059/DtsM7nj7knI51G5KCtKMbUcq8zWOsH58SI43OgVj/ddoyX/46INtwwfpGhzBv6TCliYqdpy4Vy29ZrNMdmZ8v3LVbKDiUAOGnNx8to8OwA55VgL39GLosxm2Tq5ula/iJ0ALjSut6m8dv1gny3/sSF+NpXBoI/RiZmaL207rdpTecmuM/zh/jFWFQjy4fQGFabe3F6fB71Lf7zgXrcXeSbH+/AuqkapZ4WjZ+JlW8+rS200ziJZQoLFZO2e9ifjZOTT2LfnmAoq51aRpa/9uMZV/AF8DyFuOUG/PF7WmmJqHRYlUSDc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.015266, 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, Apr 1, 2024 at 8:15=E2=80=AFAM Kairui Song wrote= : > eg. If swap_has_cache returns true, then swap cache is freed, and > skip_if_exists is set to true, __read_swap_cache_async will return > NULL for an entry that it should be able to alloc and cache, could > this be a problem (for example, causing zswap writeback to fail with > ENOMEM due to readahead)? Yeah the scenario you describe sounds plausible to me. This will make zswap writeback less efficient - it seems more pages will be (unnecessarily) skipped because of this check.