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From: Kent Overstreet To: Matthew Wilcox Cc: Vlastimil Babka , Dan Carpenter , NeilBrown , Dave Chinner , Amir Goldstein , paulmck@kernel.org, lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, linux-fsdevel , Jan Kara Subject: Re: [Lsf-pc] [LSF/MM/BPF TOPIC] Reclamation interactions with RCU Message-ID: References: <170925937840.24797.2167230750547152404@noble.neil.brown.name> <170933687972.24797.18406852925615624495@noble.neil.brown.name> <170950594802.24797.17587526251920021411@noble.neil.brown.name> <73533d54-2b92-4794-818e-753aaea887f9@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: DB02710002A X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: rebwqeynig9abywo5j5kq6mimoc8kww4 X-HE-Tag: 1710961665-786476 X-HE-Meta: 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 3XJ8Zrlv WMeWoIhRAXvi/NK36b+tkdwN+5Z82spunM2G6dz8BEggO7QK23BuqhFlA2pYHTY6yTbfNDNZwyYMYNE4UPqGKd/XOnQ== 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, Mar 20, 2024 at 06:55:36PM +0000, Matthew Wilcox wrote: > On Wed, Mar 20, 2024 at 07:48:01PM +0100, Vlastimil Babka wrote: > > On 3/20/24 19:32, Dan Carpenter wrote: > > > On Tue, Mar 12, 2024 at 03:46:32PM +0100, Vlastimil Babka wrote: > > >> But if we change it to effectively mean GFP_NOFAIL (for non-costly > > >> allocations), there should be a manageable number of places to change to a > > >> variant that allows failure. > > > > > > What does that even mean if GFP_NOFAIL can fail for "costly" allocations? > > > I thought GFP_NOFAIL couldn't fail at all... > > > > Yeah, the suggestion was that GFP_KERNEL would act as GFP_NOFAIL but only > > for non-costly allocations. Anything marked GFP_NOFAIL would still be fully > > nofail. > > GFP_NOFAIL should still fail for allocations larger than KMALLOC_MAX_SIZE. > Or should we interpret that as "die now"? Or "go into an unkillable > sleep"? If the caller really has taken the opportunity to remove their > error handling path, returning NULL will lead to a crash and a lot of > beard stroking trying to understand why a GFP_NOFAIL allocation has > returned NULL. May as well BUG_ON(size > KMALLOC_MAX_SIZE) and give > the developer a clear indication of what they did wrong. Why do we even need KMALLOC_MAX_SIZE...? Given that kmalloc internally switches to the page allocator when needed, I would think that that's something we can do away with.