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From: Kent Overstreet To: Michal Hocko Cc: Andrew Morton , Christoph Hellwig , Yafang Shao , jack@suse.cz, Christian Brauner , Alexander Viro , Paul Moore , James Morris , "Serge E. Hallyn" , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-bcachefs@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] bcachefs: do not use PF_MEMALLOC_NORECLAIM Message-ID: References: <20240826085347.1152675-1-mhocko@kernel.org> <20240826085347.1152675-2-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Stat-Signature: 5jam138mnd8w8173xi8ej5sct5cpf3uq X-Rspamd-Queue-Id: 2CCC280007 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1724706636-812851 X-HE-Meta: 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 aX9rCss3 YaiBRU0Uh+PpgOnH4EEonSKTvBOICu8Vi4hu72xUGKWK/BL5TPpMMMN/Zg5s5e3lyywIc+11cebT7o/ceutY42M/8uWDPN4D7RO2MG7W4TcMqVT7Uog+GtrPgttWrx0QzfZsViJe8vSl7dIivdVIlIfAoGXRp5UAb3eV5K+OJgyKSE+6pAJOsBOwFBYzrE1o9VVm36ms2yT1n3tfgP3azjjJ+LJ5Qg0KxqgQaDcgFrJBYzfo= 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 Mon, Aug 26, 2024 at 04:44:01PM GMT, Kent Overstreet wrote: > No, I explained why GFP_NORECLAIM/PF_MEMALLOC_NORECLAIM can absolutely > apply to a context, not a callsite, and why vmalloc() and kvmalloc() > ignoring gfp flags is a much more serious issue. > > If you want to do something useful, figure out what we're going to do > about _that_. If you really don't want PF_MEMALLOC_NORECLAIM to exist, > then see if Linus will let you plumb gfp flags down to pte allocation - > and beware, that's arch code that you'll have to fix. > > Reminder: kvmalloc() is a thing, and it's steadily seeing wider use. > > Otherwise, PF_MEMALLOC_NORECLAIM needs to stay; and thank you for > bringing this to my attention, because it's made me realize all the > other places in bcachefs that use gfp flags for allocating memory with > btree locks held need to be switch to memalloc_flags_do(). Additionally: plumbing gfp flags to pte allocation is something we do need to do. I proposed it before kvmalloc() was a thing, but now it's become much more of a lurking landmine. Even with that I'd still be against this series, though. GFP_NOFAIL interacting badly with other gfp/memalloc flags is going to continue to be an issue, and I think the only answer to that is stricter runtime checks (which, thank you mm guys for adding recently).