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Tue, 02 Jul 2024 00:00:48 -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: Barry Song <21cnbao@gmail.com> Date: Tue, 2 Jul 2024 19:00:36 +1200 Message-ID: Subject: Re: [PATCH] mm: zswap: fix zswap_never_enabled() for CONFIG_ZSWAP==N To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Barry Song , Yosry Ahmed , 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-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 977884001E X-Stat-Signature: c65gudkmja38nj9yy5znb6c39gdjctb7 X-HE-Tag: 1719903649-734266 X-HE-Meta: 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 Tb2iFyaD 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 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 Tue, Jul 2, 2024 at 6:52=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? Yes, but the API was created to inform the mm core that zswap has never bee= n enabled, allowing the mm core to perform mTHP swap-in. This is a transition= al solution until zswap supports mTHP. If zswap has been enabled, performing mTHP swap-in will result in corrupted data. You may find the answer in the mTHP swap-in series: https://lore.kernel.org/linux-mm/CAJD7tkZ4FQr6HZpduOdvmqgg_-whuZYE-Bz5O2t6y= zw6Yg+v1A@mail.gmail.com/ Thanks Barry