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[209.85.167.44]) by smtp.gmail.com with ESMTPSA id t17sm1671684lft.296.2021.09.27.12.05.13 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Sep 2021 12:05:14 -0700 (PDT) Received: by mail-lf1-f44.google.com with SMTP id e15so82015006lfr.10 for ; Mon, 27 Sep 2021 12:05:13 -0700 (PDT) X-Received: by 2002:a05:651c:1250:: with SMTP id h16mr1576330ljh.68.1632769513513; Mon, 27 Sep 2021 12:05:13 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Linus Torvalds Date: Mon, 27 Sep 2021 12:04:57 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: Struct page proposal To: Vlastimil Babka Cc: David Hildenbrand , Matthew Wilcox , Kent Overstreet , linux-fsdevel , Linux Kernel Mailing List , Linux-MM , Johannes Weiner , Andrew Morton , "Darrick J. Wong" , Christoph Hellwig , David Howells Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 27, 2021 at 11:53 AM Vlastimil Babka wrote: > > I was thinking of debug_pagealloc (unmaps free pages from direct map) but yeah, > the list is longer. In fact, the _original_ free page list was in the page itself, not in 'struct page'. The original reason to move it into 'struct page' ended up being performance, iirc. Because of how now the free page list was always in the same cache line set, the page allocator caused horrendous cache patterns on direct-mapped caches. Direct-mapped caches may thankfully be gone, and we have a lot of other things that end up having that property of "same offset within a page" just because of allocation patterns (task struct allocations being but one example), but it might still be something to try to avoid. Linus