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Thu, 15 Feb 2024 21:54:58 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id QXBuDTKIzmWKTwAAD6G6ig (envelope-from ); Thu, 15 Feb 2024 21:54:58 +0000 Date: Thu, 15 Feb 2024 22:54:53 +0100 From: Michal Hocko To: Kent Overstreet Cc: Vlastimil Babka , Suren Baghdasaryan , akpm@linux-foundation.org, hannes@cmpxchg.org, roman.gushchin@linux.dev, mgorman@suse.de, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, 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, 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, shakeelb@google.com, songmuchun@bytedance.com, jbaron@akamai.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 v3 31/35] lib: add memory allocations report in show_mem() Message-ID: References: <20240212213922.783301-1-surenb@google.com> <20240212213922.783301-32-surenb@google.com> <320cd134-b767-4f29-869b-d219793ba8a1@suse.cz> Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; 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RCVD_TLS_ALL(0.00)[]; SUSPICIOUS_RECIPS(1.50)[] X-Spam-Score: -2.51 X-Rspamd-Queue-Id: 6268E1FB3E X-Spam-Flag: NO On Thu 15-02-24 15:33:30, Kent Overstreet wrote: > On Thu, Feb 15, 2024 at 09:22:07PM +0100, Vlastimil Babka wrote: > > On 2/15/24 19:29, Kent Overstreet wrote: > > > On Thu, Feb 15, 2024 at 08:47:59AM -0800, Suren Baghdasaryan wrote: > > >> On Thu, Feb 15, 2024 at 8:45 AM Michal Hocko wrote: > > >> > > > >> > On Thu 15-02-24 06:58:42, Suren Baghdasaryan wrote: > > >> > > On Thu, Feb 15, 2024 at 1:22 AM Michal Hocko wrote: > > >> > > > > > >> > > > On Mon 12-02-24 13:39:17, Suren Baghdasaryan wrote: > > >> > > > [...] > > >> > > > > @@ -423,4 +424,18 @@ void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx) > > >> > > > > #ifdef CONFIG_MEMORY_FAILURE > > >> > > > > printk("%lu pages hwpoisoned\n", atomic_long_read(&num_poisoned_pages)); > > >> > > > > #endif > > >> > > > > +#ifdef CONFIG_MEM_ALLOC_PROFILING > > >> > > > > + { > > >> > > > > + struct seq_buf s; > > >> > > > > + char *buf = kmalloc(4096, GFP_ATOMIC); > > >> > > > > + > > >> > > > > + if (buf) { > > >> > > > > + printk("Memory allocations:\n"); > > >> > > > > + seq_buf_init(&s, buf, 4096); > > >> > > > > + alloc_tags_show_mem_report(&s); > > >> > > > > + printk("%s", buf); > > >> > > > > + kfree(buf); > > >> > > > > + } > > >> > > > > + } > > >> > > > > +#endif > > >> > > > > > >> > > > I am pretty sure I have already objected to this. Memory allocations in > > >> > > > the oom path are simply no go unless there is absolutely no other way > > >> > > > around that. In this case the buffer could be preallocated. > > >> > > > > >> > > Good point. We will change this to a smaller buffer allocated on the > > >> > > stack and will print records one-by-one. Thanks! > > >> > > > >> > __show_mem could be called with a very deep call chains. A single > > >> > pre-allocated buffer should just do ok. > > >> > > >> Ack. Will do. > > > > > > No, we're not going to permanently burn 4k here. > > > > > > It's completely fine if the allocation fails, there's nothing "unsafe" > > > about doing a GFP_ATOMIC allocation here. > > > > Well, I think without __GFP_NOWARN it will cause a warning and thus > > recursion into __show_mem(), potentially infinite? Which is of course > > trivial to fix, but I'd myself rather sacrifice a bit of memory to get this > > potentially very useful output, if I enabled the profiling. The necessary > > memory overhead of page_ext and slabobj_ext makes the printing buffer > > overhead negligible in comparison? > > __GFP_NOWARN is a good point, we should have that. > > But - and correct me if I'm wrong here - doesn't an OOM kick in well > before GFP_ATOMIC 4k allocations are failing? Not really, GFP_ATOMIC users can compete with reclaimers and consume those reserves. > I'd expect the system to > be well and truly hosed at that point. It is OOMed... > If we want this report to be 100% reliable, then yes the preallocated > buffer makes sense - but I don't think 100% makes sense here; I think we > can accept ~99% and give back that 4k. Think about that from the memory reserves consumers. The atomic reserve is a scarse resource and now you want to use it for debugging purposes for which you could have preallocated. -- Michal Hocko SUSE Labs