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[209.85.208.178]) by smtp.gmail.com with ESMTPSA id s1sm3107579lfi.76.2020.08.06.11.32.36 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Aug 2020 11:32:37 -0700 (PDT) Received: by mail-lj1-f178.google.com with SMTP id z14so15303546ljm.1 for ; Thu, 06 Aug 2020 11:32:36 -0700 (PDT) X-Received: by 2002:a2e:b008:: with SMTP id y8mr3902152ljk.421.1596738756512; Thu, 06 Aug 2020 11:32:36 -0700 (PDT) MIME-Version: 1.0 References: <20200724152424.GC17209@redhat.com> <20200725101445.GB3870@redhat.com> <20200806180024.GB17456@casper.infradead.org> In-Reply-To: <20200806180024.GB17456@casper.infradead.org> From: Linus Torvalds Date: Thu, 6 Aug 2020 11:32:20 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH] mm: silence soft lockups from unlock_page To: Matthew Wilcox Cc: Hugh Dickins , Oleg Nesterov , Michal Hocko , Linux-MM , LKML , Andrew Morton , Tim Chen , Michal Hocko , Greg KH Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 244C81819E769 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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: On Thu, Aug 6, 2020 at 11:00 AM Matthew Wilcox wrote: > > It wasn't clear to me whether Hugh thought it was an improvement or > not that trylock was now less likely to jump the queue. There're > the usual "fair is the opposite of throughput" kind of arguments. Yeah, it could go either way. But on the whole, if the lock bit is getting any contention, I think we'd rather have it be fair for latency reasons. That said, I'm not convinced about my patch, and I actually threw it away without even testing it (sometimes I keep patches around in my private tree for testing, and they can live there for months or even years when I wonder if they are worth it, but this time I didn't bother to go to the trouble). If somebody is interested in pursuing this, I think that patch might be a good starting point (and it _might_ even work), but it seemed to be too subtle to really worry about unless somebody finds an actual acute reason for it. I think the existing patch narrowing the window is good, and it clearly didn't hurt throughput (although that was almost certainly for other reasons). Linus