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[2603:7000:c01:2716:8f57:5681:ccd3:4a2e]) by smtp.gmail.com with ESMTPSA id f5-20020ac840c5000000b003e0945575dasm373105qtm.1.2023.05.09.10.44.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 May 2023 10:44:02 -0700 (PDT) Date: Tue, 9 May 2023 13:44:01 -0400 From: Johannes Weiner To: Sergey Senozhatsky Cc: Nhat Pham , Minchan Kim , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ngupta@vflare.org, sjenning@redhat.com, ddstreet@ieee.org, vitaly.wool@konsulko.com, kernel-team@meta.com Subject: Re: [PATCH] zsmalloc: move LRU update from zs_map_object() to zs_malloc() Message-ID: <20230509174401.GA18828@cmpxchg.org> References: <20230505185054.2417128-1-nphamcs@gmail.com> <20230506030140.GC3281499@google.com> <20230508140658.GA3421@cmpxchg.org> <20230509030030.GD11511@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230509030030.GD11511@google.com> X-Rspamd-Queue-Id: D907C40009 X-Rspam-User: X-Rspamd-Server: rspam06 X-Stat-Signature: mk8c3yrtpqre3hs88c9qtb6r6uk7enkg X-HE-Tag: 1683654243-427554 X-HE-Meta: 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 OeI6xqIL 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.009666, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, May 09, 2023 at 12:00:30PM +0900, Sergey Senozhatsky wrote: > On (23/05/08 09:00), Nhat Pham wrote: > > > The deeper bug here is that zs_map_object() tries to add the page to > > > the LRU list while the shrinker has it isolated for reclaim. This is > > > way too sutble and error prone. Even if it worked now, it'll cause > > > corruption issues down the line. > > > > > > For example, Nhat is adding a secondary entry point to reclaim. > > > Reclaim expects that a page that's on the LRU is also on the fullness > > > list, so this would lead to a double remove_zspage() and BUG_ON(). > > > > > > This patch doesn't just fix the crash, it eliminates the deeper LRU > > > isolation issue and makes the code more robust and simple. > > > > I agree. IMO, less unnecessary concurrent interaction is always a > > win for developers' and maintainers' cognitive load. > > Thanks for all the explanations. > > > As a side benefit - this also gets rid of the inelegant check > > (mm == ZS_MM_WO). The fact that we had to include a > > a multi-paragraph explanation for a 3-line piece of code > > should have been a red flag. > > Minchan had some strong opinion on that, so we need to hear from him > before we decide how do we fix it. I'd be happy if he could validate the fix. But this fixes a crash, so the clock is ticking. I will also say, his was a design preference. One we agreed to only very reluctantly: https://lore.kernel.org/lkml/Y3f6habiVuV9LMcu@google.com/ Now we have a crash that is a direct result of it, and which cost us (and apparently is still costing us) time and energy to resolve. Unless somebody surfaces a real technical problem with the fix, I'd say let's do it our way this time.