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[109.81.89.238]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a9a68c27893sm93408266b.195.2024.10.18.06.03.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Oct 2024 06:03:43 -0700 (PDT) Date: Fri, 18 Oct 2024 15:03:43 +0200 From: Michal Hocko To: Suren Baghdasaryan Cc: David Hildenbrand , John Hubbard , Yosry Ahmed , akpm@linux-foundation.org, kent.overstreet@linux.dev, corbet@lwn.net, arnd@arndb.de, mcgrof@kernel.org, rppt@kernel.org, paulmck@kernel.org, thuth@redhat.com, tglx@linutronix.de, bp@alien8.de, xiongwei.song@windriver.com, ardb@kernel.org, vbabka@suse.cz, hannes@cmpxchg.org, roman.gushchin@linux.dev, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, pasha.tatashin@soleen.com, souravpanda@google.com, keescook@chromium.org, dennis@kernel.org, yuzhao@google.com, vvvvvv@google.com, rostedt@goodmis.org, iamjoonsoo.kim@lge.com, rientjes@google.com, minchan@google.com, kaleshsingh@google.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-modules@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v3 5/5] alloc_tag: config to store page allocation tag refs in page flags Message-ID: References: <20241014203646.1952505-1-surenb@google.com> <20241014203646.1952505-6-surenb@google.com> <6a2a84f5-8474-432f-b97e-18552a9d993c@redhat.com> <9c81a8bb-18e5-4851-9925-769bf8535e46@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspam-User: X-Stat-Signature: xrhediku1epw33pytq577fe9yyef4wjo X-Rspamd-Queue-Id: 714D9A0012 X-Rspamd-Server: rspam11 X-HE-Tag: 1729256615-810629 X-HE-Meta: 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 hYa34iSl Zvcjgf7iWGmPAp42QKY2I5g68OzTsJA6xujZcGqqQlyXTEVBopODHBCbM4CIYD/1caEcfCvenC9j1zrNuJRpko7f1VOdFejr44hQJLu0zoCi2tNRbCd7TvzLqD8gznafIM9+CdZ5fbAuJOgJug7ffZZSRmNZDudgv3eoMwe6Jah4HUhdpo/wjJBO6rdV8MZcZWY6lxBmpTDZyH2Rj8afyrhecngXquTbn0+mtTwm0eFzwZdRvpcb4jz5hCoRGFLP0EDeBExNytqmKCqxLFosLWef+Ol7YUjiSPRj/v6QiNpizqkFLEl/uTvj23632YvBHWjpIb5y1e3H9agd3qGMWlc6OrSzbYiKEVFOlCa+oxAYjJQ2n3Od8pQiMiyhb8Z1IkKlVdj36krqSNgpoKWvDqTN7fg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, 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 15-10-24 08:58:59, Suren Baghdasaryan wrote: > On Tue, Oct 15, 2024 at 8:42 AM David Hildenbrand wrote: [...] > > Right, I think what John is concerned about (and me as well) is that > > once a new feature really needs a page flag, there will be objection > > like "no you can't, we need them for allocation tags otherwise that > > feature will be degraded". > > I do understand your concern but IMHO the possibility of degrading a > feature should not be a reason to always operate at degraded capacity > (which is what we have today). If one is really concerned about > possible future regression they can set > CONFIG_PGALLOC_TAG_USE_PAGEFLAGS=n and keep what we have today. That's > why I'm strongly advocating that we do need > CONFIG_PGALLOC_TAG_USE_PAGEFLAGS so that the user has control over how > this scarce resource is used. I really do not think users will know how/why to setup this and I wouldn't even bother them thinking about that at all TBH. This is an implementation detail. It is fine to reuse unused flags space as a storage as a performance optimization but why do you want users to bother with that? Why would they ever want to say N here? -- Michal Hocko SUSE Labs