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[109.81.94.157]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a7a3c78611asm649739666b.45.2024.07.24.06.31.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Jul 2024 06:31:43 -0700 (PDT) Date: Wed, 24 Jul 2024 15:31:42 +0200 From: Michal Hocko To: Christoph Hellwig Cc: Vlastimil Babka , Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, 42.hyeyoo@gmail.com, cl@linux.com, iamjoonsoo.kim@lge.com, lstoakes@gmail.com, penberg@kernel.org, rientjes@google.com, roman.gushchin@linux.dev, urezki@gmail.com, v-songbaohua@oppo.com, virtualization@lists.linux.dev, hailong.liu@oppo.com, torvalds@linux-foundation.org Subject: Re: [PATCH RFC 5/5] non-mm: discourage the usage of __GFP_NOFAIL and encourage GFP_NOFAIL Message-ID: References: <20240724085544.299090-1-21cnbao@gmail.com> <20240724085544.299090-6-21cnbao@gmail.com> <68ee812b-3b96-4c8b-9a54-70d4742488bb@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 5aohmdru3z6h1ir1oe74jdt1kgjmithj X-Rspam-User: X-Rspamd-Queue-Id: AE148180028 X-Rspamd-Server: rspam02 X-HE-Tag: 1721827905-194189 X-HE-Meta: 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 iZ+yMDaX YlNofsm3QzM/gsikGjza2upO5e7rWuIWp5PL08Rz10YUqZ+/tboQMWWrX5HqlDBr2nfrKLQNOdsLyZ8erwm9EWuubX9vh1bHxt2BS9Lj5DqDEAXm9lcoaMKH959IpCztjblx8CWNJKuCx/LLIKbfJ4y15fKD2E5jUEFhbVaEC7ghzdJE8fcE4pKaPaoDKzvizJR999vsDBY1W6uqFuHdRalJZbUrTeA3kgxSE37RYdp45HURPPk8cZbc5m8olFAvs7aNknIZC9et7IETnhV6oGRbwdn+6iMa3fJgivHDuaF7b7UklTSBVc5WpfTV7ELUQvyZ9zw2gOJfzPrN1hc8+W63o19vW0X6A86ag5xH/mmU/xpP9tAxxO1+h4RDsGX2dMDiIa8kleOkO/ZCe8+YDDqFixQ== 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 Wed 24-07-24 06:23:29, Christoph Hellwig wrote: > On Wed, Jul 24, 2024 at 03:21:13PM +0200, Michal Hocko wrote: > > Scope API is tricky here. Exactly because the scope itself could have > > opportunistic GFP_NOWAIT allocations. > > Really, where? That just sounds f**cked up as callers using any kind > of nofail API can be broken by a caller higher in the stack. I do not see this a problem. There is no real reason to have a NOWAIT allocation down the stack that has a different fallback strategy. I am not saying that this is the current practice because I do not know that but I am saying that this is not impossible to imagine and it makes scoped NOFAIL context subtle and error prone. > And that's totally independ of adding a NOFS/NOIO helper, so it'll need > to be fixed. > > Adding more NOFS/NOIO wrappers while we're trying to kill the flag just > is not helpful going forward. NOFS, NOIO scopes are both compatible with NOFAIL and NOWAIT contexts. -- Michal Hocko SUSE Labs