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[109.81.83.166]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-429ded5c166sm11604145e9.46.2024.08.14.00.42.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Aug 2024 00:42:04 -0700 (PDT) Date: Wed, 14 Aug 2024 09:42:03 +0200 From: Michal Hocko To: Yafang Shao Cc: Christoph Hellwig , akpm@linux-foundation.org, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, david@fromorbit.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Kent Overstreet Subject: Re: [PATCH 1/2] mm: Add memalloc_nowait_{save,restore} Message-ID: References: <20240812090525.80299-1-laoar.shao@gmail.com> <20240812090525.80299-2-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 85DED180018 X-Stat-Signature: cygoyb8xufmxdm8p4knya4s5sxedy4mt X-HE-Tag: 1723621326-345349 X-HE-Meta: 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 btjIanq8 jalMqKC+SIGdivKkm4XneoRsQVMpe+J1TtwyDZR2JRYuqJnEtoeGlYIxDylgoxcI9e0fhW6QSJLjgVzn+81sRsKDOBzHu6SGAjXtrllEVUmxC+1OFu9FAKbOvg0iMlcgEdXOxOmShu6ysyeeLe+D9+091N6BEL44ArStv/R/wkP8WuN0ryqGA1OCMYc31AVVaPkStbKOffTuBEhjObsvZ4hcpnR4frAPTWuuaRfY54eGcj7WODlUChpxiNu5MXtb7a9Ymy4yTTOYxi6NxRUOqQiIHdO8kDHfGIi2jNhdFVRQGF5668G8n+NchgaYoyjUpYip57dZGyZbzSM925xAuwxiJvv+0Sz3+cGKz0XG/8GRQiI5rq/bcXUh2CoaC/tB8daQ0sxH5aJTYkPGUB9/0bflYqXjM7v3QtUDhW6m5IiZpf/1QQKbHJljoPjLJ8kNV2yrrRZfy73XFJn2iqqyTbAXFPnLf05Wn2a1+v/3mhdXkvI4= X-Bogosity: Ham, tests=bogofilter, spamicity=0.007545, 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 12-08-24 20:59:53, Yafang Shao wrote: > On Mon, Aug 12, 2024 at 7:37 PM Christoph Hellwig wrote: > > > > On Mon, Aug 12, 2024 at 05:05:24PM +0800, Yafang Shao wrote: > > > The PF_MEMALLOC_NORECLAIM flag was introduced in commit eab0af905bfc > > > ("mm: introduce PF_MEMALLOC_NORECLAIM, PF_MEMALLOC_NOWARN"). To complement > > > this, let's add two helper functions, memalloc_nowait_{save,restore}, which > > > will be useful in scenarios where we want to avoid waiting for memory > > > reclamation. > > > > No, forcing nowait on callee contets is just asking for trouble. > > Unlike NOIO or NOFS this is incompatible with NOFAIL allocations > > I don’t see any incompatibility in __alloc_pages_slowpath(). The > ~__GFP_DIRECT_RECLAIM flag only ensures that direct reclaim is not > performed, but it doesn’t prevent the allocation of pages from > ALLOC_MIN_RESERVE, correct? Right but this means that you just made any potential nested allocation within the scope that is GFP_NOFAIL a busy loop essentially. Not to mention it BUG_ON as non-sleeping GFP_NOFAIL allocations are unsupported. I believe this is what Christoph had in mind. I am really surprised that we even have PF_MEMALLOC_NORECLAIM in the first place! Unsurprisingly this was merged without any review by the MM community :/ -- Michal Hocko SUSE Labs