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From: Kent Overstreet To: Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Qi Zheng , Roman Gushchin Subject: Re: [PATCH 4/7] mm: Centralize & improve oom reporting in show_mem.c Message-ID: <20231128175439.6jarreie7cay74fn@moria.home.lan> References: <20231122232515.177833-1-kent.overstreet@linux.dev> <20231122232515.177833-5-kent.overstreet@linux.dev> 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: 9BCFD100019 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: gn83p5hssi15b8igdg9h8ge1kxb7d4mu X-HE-Tag: 1701194084-217517 X-HE-Meta: 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 yC8MMrY4 b0IByYDVvyDoNlMYtHSxspoj9xHMKwmsfrC4AP1bX1UTYZmygJjrN4LcVXfsApaSMMxWGQcVaydDTLRpM4IEcDnrhO+czfqRRIMqK 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 Tue, Nov 28, 2023 at 11:07:18AM +0100, Michal Hocko wrote: > On Wed 22-11-23 18:25:09, Kent Overstreet wrote: > [...] > > 00177 Shrinkers: > > 00177 super_cache_scan: objects: 127 > > 00177 super_cache_scan: objects: 106 > > 00177 jbd2_journal_shrink_scan: objects: 32 > > 00177 ext4_es_scan: objects: 32 > > 00177 bch2_btree_cache_scan: objects: 8 > > 00177 nr nodes: 24 > > 00177 nr dirty: 0 > > 00177 cannibalize lock: 0000000000000000 > > 00177 > > 00177 super_cache_scan: objects: 8 > > 00177 super_cache_scan: objects: 1 > > It would be really great to provide an example on how these numbers are > useful for the oom evaluation. I should've posted an example from the end of the patch series; I'll do that later today. > [...] > > @@ -423,4 +426,21 @@ 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 > > + > > + buf = kmalloc(4096, GFP_ATOMIC); > > I really do not think we want to allow allocations from the OOM context. > Is there any reason why this cannot be a statically allocated buffer? You've made this claim before without ever giving any reasoning behind it. It's GFP_ATOMIC; it has to work from _interrupt_ context, OOM context is fine. And no, we don't want to burn 4k on a static buffer that is almost never used; people do care about making the kernel run on small systems.