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AJvYcCW5aEUduEEvbHX+SxUpckXVpuOe984wIiLc8SvCDMohYWiANDHlyh0tsg04v22IoRcwtkWhN5aldgYsdJ53kp6s8nU= X-Gm-Message-State: AOJu0YxRpNeLZ/I620B6i3yprin/01c2MEm72fYugLafWcEmAHv3Dp64 WhbAl6XRpzMKyl2hiF+Fzq2yhj7hJT0954fL1/jLiFxKme8XcHFGo1i8n6/TseghNHxoayiBJMn l1ItPFKztEBYQ2mVTPbMpqX5sqCE= X-Google-Smtp-Source: AGHT+IEddrkcciPyjk/jy+C8jOOvaiscpFh798lcV3tGhcixFJW2X9gXquf54JGBLgptrXGl/+0cokSrTnar1XabApQ= X-Received: by 2002:a05:6122:4124:b0:4d3:31fc:4839 with SMTP id 71dfb90a1353d-4eb5621b763mr4657457e0c.2.1717802921472; Fri, 07 Jun 2024 16:28:41 -0700 (PDT) MIME-Version: 1.0 References: <20240606184818.1566920-1-yosryahmed@google.com> <84d78362-e75c-40c8-b6c2-56d5d5292aa7@redhat.com> <7507d075-9f4d-4a9b-836c-1fbb2fbd2257@redhat.com> <9374758d-9f81-4e4f-8405-1f972234173e@redhat.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Sat, 8 Jun 2024 06:28:21 +0800 Message-ID: Subject: Re: [PATCH] mm: zswap: add VM_BUG_ON() if large folio swapin is attempted To: Yosry Ahmed Cc: David Hildenbrand , Andrew Morton , Johannes Weiner , Nhat Pham , Chengming Zhou , Baolin Wang , Chris Li , Ryan Roberts , Matthew Wilcox , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 8E18E80002 X-Stat-Signature: n86315j8jz4yyi1bxjnmrwwkc5tpxqss X-HE-Tag: 1717802922-158243 X-HE-Meta: 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 KT25MC2Z 9MUyVbu9t2cwVPfhaPY4P1WRzzU5PEBP4QlXL3h6Ej4SD6F5qbXfqQBoisKFuQ1EjWnkEG1CCSG4m3k7Z7SdT49vhFw2DM8lW8nIi8dHAEkdxXiAIuM3dvzRZNaWV3Kcq8KA55iIdjKLWNdaTdFZGIEqYtAAgjNnISAw2iojRdG3Hf6cTEieMQYazm4VC+GEeUaZ0STbT0XQI+CHJPCTHAhhKk42+Bcp9s5ytbv64PU7xJ0BZ8mvW1HJm8MJyPZO/v1+2epLs4V0nHS+M8PfhwAKAuRyoUCr3/odXW6029zI0+QOAIlpzRvIpRq+SSLB6uiVD0xczcmPMBpAws23uKbyRT7HYKv9ckydZLH/HFLSXzLUpYCrVeA7PqO02oQ4Fyjqoua2sVNv2XeRuAdb18kH0D6E9OUyynnfDWRQJJS+1H2s= 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 Sat, Jun 8, 2024 at 7:17=E2=80=AFAM Yosry Ahmed = wrote: > > [..] > > > One problem is that even if zswap was never enabled, the warning will > > > be emitted just if CONFIG_ZSWAP is on. Perhaps we need a variable or > > > static key if zswap was "ever" enabled. > > > > > > Barry, I suspect your is_zswap_enabled() check is deficient for > > > similar reasons, zswap could have been enabled before then became > > > disabled. > > > > I don't understand this. if zswap was enabled before but is disabled wh= en > > I am loading data, will I get corrupted data before zswap was once enab= led? > > If not, it seems nothing important. > > If zswap was enabled and then disabled, some pages may still be in > zswap. We do not load the pages from zswap when it is disabled, we > just stop storing new pages. > > So if you just rely in checking whether zswap is enabled at swapin > time to decide whether to use large folios, you may end up with a > situation where zswap is disabled, yet parts of the large folio you > are trying to swapin (or all of it) is in zswap. > > This is why I think we'll need to track whether zswap was ever enabled > instead (or if a page was ever stored). Thanks! It doesn't seem good. Do we have a simple way to clean zswap when it is disabled? seems not easy? Just like we do swapoff, or disable cache, we ensure they are clean - this is a real "disable". Thanks Barry