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[209.85.218.47]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a5a25f0d2a9sm589855466b.60.2024.05.13.10.34.03 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 May 2024 10:34:04 -0700 (PDT) Received: by mail-ej1-f47.google.com with SMTP id a640c23a62f3a-a59b58fe083so1001235466b.0 for ; Mon, 13 May 2024 10:34:03 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCUacgcIxIf7j6ZaAYLH5Yq+gmA5smjoNe4LTqrf8eT3kLfqlEBUTuOYnL4Ri94bUiJsuvkuJKkc4k+8bcw8NE3gZiI= X-Received: by 2002:a17:906:2298:b0:a5a:3579:b908 with SMTP id a640c23a62f3a-a5a3579bb63mr599168266b.38.1715621643624; Mon, 13 May 2024 10:34:03 -0700 (PDT) MIME-Version: 1.0 References: <587f5e6b-d543-4028-85c8-93cc8f581d02@suse.cz> In-Reply-To: <587f5e6b-d543-4028-85c8-93cc8f581d02@suse.cz> From: Linus Torvalds Date: Mon, 13 May 2024 10:33:46 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [GIT PULL] slab updates for 6.10 To: Vlastimil Babka Cc: David Rientjes , Joonsoo Kim , Christoph Lameter , Pekka Enberg , Andrew Morton , "linux-mm@kvack.org" , LKML , patches@lists.linux.dev, Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Chengming Zhou Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 905C220011 X-Stat-Signature: 866j18a38au9kyrr8ubfbcafcretsugu X-HE-Tag: 1715621646-709678 X-HE-Meta: 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 ijyd+5De 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000384, 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 Thu, 9 May 2024 at 07:25, Vlastimil Babka wrote: > > To avoid affecting fast paths with another shared counter (attempted in the > past) or complex partial list traversal schemes that allow rescheduling, the > chosen solution resorts to approximation - when the partial list is over > 10000 slabs long, we will only traverse first 5000 slabs from head and tail > each and use the average of those to estimate the whole list. Both head and > tail are used as the slabs near head to tend to have more free objects than > the slabs towards the tail. I suspect you could have cut this down by an order of magnitude, and made the limit be just 1k slabs rather than 10k slabs. Or even _another_ order of magnitude smaller. Somebody was being a bit too worried about approximations, methinks - but I think the real worry goes the other way, where it's practically so hard to even hit the approximation situation that it gets no testing at all. IOW, I suspect it's better to be explicit about approximations, and have people aware of it, rather than be overly cautious and have it be a special case that almost never triggers in any normal loads. But pulled. Linus