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b=I/+f4ipYS7WoxO43yMqiWlwu3V3hgu2UIl6NOWmGnbai7wVyb7QXGe9mLtzYpH5U8 oYorKoy4dDax3OQt45+2sWuCfC8j8ptBDiqVkPmpdACTJO2rLAIVkWeZf5mFhbTOcN N7zRMVFrruzjy3eNKzyG0Wc3uOznuESFycfp3Hfk= Date: Tue, 2 Jul 2024 19:02:24 -0700 From: Andrew Morton To: Yosry Ahmed 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 Subject: Re: [PATCH] mm: zswap: fix zswap_never_enabled() for CONFIG_ZSWAP==N Message-Id: <20240702190224.99d97227a02bbbe4f140f845@linux-foundation.org> In-Reply-To: References: <20240629232231.42394-1-21cnbao@gmail.com> <20240701235210.5c187c85aa225292d034cafc@linux-foundation.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: B776E80012 X-Stat-Signature: gijc7jky9bzedsrbbdrxe1b7t9az61ux X-Rspam-User: X-HE-Tag: 1719972149-440584 X-HE-Meta: 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 vwQpPrKe /bHten3lnT0+53NobAYC4X8CUxydlyCX49+xHynkwQesOIJNri8ttWD9OBTGLPg/wVVmANIMyynv5R84hR4IMHl3PY1O5+/wFT9LyTsHhxNVVenmfBupLpmWO3jCEvXtEXFKShKx7nFLlzIDdXMipOuWndHoj6X9bb2i0OfA1mf9u3zN46WaKy/8sZ46X+Jn03af5cwGUAPFRE4QyX+M9/a7tX/u84tkNoqtvzWM7KTERkHEor5z3wLe1BVt9En0TEhR9XPDQrgpX3ACIIVS4BHIVcj7r0ETZpeH/jMNijHqEQUA= 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, 2 Jul 2024 04:58:05 -0700 Yosry Ahmed wrote: > > > --- 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. OK, thanks, I added this to the changelog: The only effect of this issue is that with Barry's latest large folio swapin patches for zram ("mm: support mTHP swap-in for zRAM-like swapfile"), we will always fallback to order-0 swapin, even mistakenly when !CONFIG_ZSWAP. Basically this bug makes Barry's in progress patches not work at all.