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AJvYcCUJvWPslK0EO7n45a0TUPb2fDznpane3CtK9K8/LNZG1TlJVL/KT2dXObsc+MQvt7E3QSiXhjqN3q7ydzyWgLJ3iXg= X-Gm-Message-State: AOJu0YwDkfFAjnSB2M3SNJ69iz9tCDNOr2NdcKYbgUosepVO5sXeQ389 4KUD/6d9d/twT/vHPNpdfrixF9iDGTv9zMYEgT4OA+yBknbmyQB/9tspT2Fevl0cAECVaardYy4 GsKsn/SmXPj//yDFf8SBr4zsTbNvMNX/LLKIf X-Google-Smtp-Source: AGHT+IEgm5z95cSGFxQ3V0ayY7Ai0asCW3V+jsOOSHTXOTWqh+9MPajWk+OvayBaKI3FNgoXefKdwE6XKrFDcgHdCBk= X-Received: by 2002:a17:907:724d:b0:a6f:b84e:8454 with SMTP id a640c23a62f3a-a751443c63emr627377266b.11.1719921524083; Tue, 02 Jul 2024 04:58:44 -0700 (PDT) MIME-Version: 1.0 References: <20240629232231.42394-1-21cnbao@gmail.com> <20240701235210.5c187c85aa225292d034cafc@linux-foundation.org> In-Reply-To: <20240701235210.5c187c85aa225292d034cafc@linux-foundation.org> From: Yosry Ahmed Date: Tue, 2 Jul 2024 04:58:05 -0700 Message-ID: Subject: Re: [PATCH] mm: zswap: fix zswap_never_enabled() for CONFIG_ZSWAP==N To: Andrew Morton Cc: Barry Song <21cnbao@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Barry Song , Nhat Pham , Chengming Zhou , Chris Li , David Hildenbrand , Johannes Weiner , Matthew Wilcox Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 2F1E51C0003 X-Stat-Signature: n8pwsrn93y7jzhqiresnbr1fo8uxu78o X-HE-Tag: 1719921525-448701 X-HE-Meta: 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 WDAY368d PRbywnSd0qCQe16oGIiGkLrp4NYHkgX82pILNNHQF8bygjZA90XRMwhBZ4uaJIqHdJ1WOgcbqiPlImt6iMeuCTAVWTQOBAJJ+2O2yZ/vBVUy8dLapyZc7ehDfSGiSyYCnHmn+wd0IvP/j8bUTwjM4YjuEGvmANyGVC5uxHz2Imz7i2aO1EdkY4iYfMtzCOdaU/5M5P5acQ75gwxQcdtIqWW7Q47hQfbwO2Cacf8iu4P9L2YgaV7NYRKel32ZOKqrTHBZ7+BzMaByew+il8BHG0TsJN8HsJ6hKbmAzYceYwKaMe4dUr3wpnfds3+7SNFFovWAVWx17BNdRHwDSQXWo+xoqhTtXIRBCrKwu 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, Jul 1, 2024 at 11:52=E2=80=AFPM Andrew Morton wrote: > > On Sun, 30 Jun 2024 11:22:31 +1200 Barry Song <21cnbao@gmail.com> wrote: > > > From: Barry Song > > > > If CONFIG_ZSWAP is set to N, it means zswap cannot be enabled. > > zswap_never_enabled() should return true. > > > > ... > > > > --- a/include/linux/zswap.h > > +++ b/include/linux/zswap.h > > @@ -68,7 +68,7 @@ static inline bool zswap_is_enabled(void) > > > > static inline bool zswap_never_enabled(void) > > { > > - return false; > > + return true; > > } > > Well, that code was as wrong as it's possible to get. > > But what effect does this have? Seems "not much"? Perhaps we'll > attempt a zswap_load() which later fails for other reasons? Actually zswap_load() is a noop with !CONFIG_ZSWAP, so it doesn't have an effect there. The only effect is that with Barry's latest large folio swapin patches for zram, we will always fallback to order-0 swapin, even mistakenly when !CONFIG_ZSWAP. Basically the bug just makes Barry's in progress patches not work at all.