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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rnLpl-00000007AzI-40SJ; Thu, 21 Mar 2024 17:04:06 +0000 Date: Thu, 21 Mar 2024 17:04:05 +0000 From: Matthew Wilcox To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, kent.overstreet@linux.dev, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, roman.gushchin@linux.dev, mgorman@suse.de, dave@stgolabs.net, liam.howlett@oracle.com, penguin-kernel@i-love.sakura.ne.jp, corbet@lwn.net, void@manifault.com, peterz@infradead.org, juri.lelli@redhat.com, catalin.marinas@arm.com, will@kernel.org, arnd@arndb.de, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, peterx@redhat.com, david@redhat.com, axboe@kernel.dk, mcgrof@kernel.org, masahiroy@kernel.org, nathan@kernel.org, dennis@kernel.org, jhubbard@nvidia.com, tj@kernel.org, muchun.song@linux.dev, rppt@kernel.org, paulmck@kernel.org, pasha.tatashin@soleen.com, yosryahmed@google.com, yuzhao@google.com, dhowells@redhat.com, hughd@google.com, andreyknvl@gmail.com, keescook@chromium.org, ndesaulniers@google.com, vvvvvv@google.com, gregkh@linuxfoundation.org, ebiggers@google.com, ytcoode@gmail.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, bristot@redhat.com, vschneid@redhat.com, cl@linux.com, penberg@kernel.org, iamjoonsoo.kim@lge.com, 42.hyeyoo@gmail.com, glider@google.com, elver@google.com, dvyukov@google.com, songmuchun@bytedance.com, jbaron@akamai.com, aliceryhl@google.com, rientjes@google.com, minchan@google.com, kaleshsingh@google.com, kernel-team@android.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, iommu@lists.linux.dev, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-modules@vger.kernel.org, kasan-dev@googlegroups.com, cgroups@vger.kernel.org Subject: Re: [PATCH v6 20/37] mm: fix non-compound multi-order memory accounting in __free_pages Message-ID: References: <20240321163705.3067592-1-surenb@google.com> <20240321163705.3067592-21-surenb@google.com> Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Mar 21, 2024 at 04:48:53PM +0000, Matthew Wilcox wrote: > On Thu, Mar 21, 2024 at 09:36:42AM -0700, Suren Baghdasaryan wrote: > > +++ b/mm/page_alloc.c > > @@ -4700,12 +4700,15 @@ void __free_pages(struct page *page, unsigned int order) > > { > > /* get PageHead before we drop reference */ > > int head = PageHead(page); > > + struct alloc_tag *tag = pgalloc_tag_get(page); > > > > if (put_page_testzero(page)) > > free_the_page(page, order); > > - else if (!head) > > + else if (!head) { > > + pgalloc_tag_sub_pages(tag, (1 << order) - 1); > > while (order-- > 0) > > free_the_page(page + (1 << order), order); > > + } > > Why do you need these new functions instead of just: > > + else if (!head) { > + pgalloc_tag_sub(page, (1 << order) - 1); > while (order-- > 0) > free_the_page(page + (1 << order), order); > + } Actually, I'm not sure this is safe (I don't fully understand codetags, so it may be safe). What can happen is that the put_page() can come in before the pgalloc_tag_sub(), and then that page can be allocated again. Will that cause confusion?