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[2003:cb:c704:7c00:aaa9:2ce5:5aa0:f736]) by smtp.gmail.com with ESMTPSA id l36-20020a05600c08a400b003942a244f48sm10240715wmp.33.2022.05.30.09.54.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 30 May 2022 09:54:26 -0700 (PDT) Message-ID: Date: Mon, 30 May 2022 18:54:25 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: Freeing page flags To: Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org References: From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: D417E12004D X-Rspam-User: Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=EbUbkwAT; spf=none (imf29.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: xbgs18byb194re7tgbeado8cte47jpqu X-Rspamd-Server: rspam05 X-HE-Tag: 1653929657-656966 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 12.05.22 22:54, Matthew Wilcox wrote: > The LWN writeup [1] on merging the MGLRU reminded me that I need to send > out a plan for removing page flags that we can do without. > > 1. PG_error. It's basically useless. If the page was read successfully, > PG_uptodate is set. If not, PG_uptodate is clear. The page cache > doesn't use PG_error. Some filesystems do, and we need to transition > them away from using it. > > 2. PG_private. This tells us whether we have anything stored at > page->private. We can just check if page->private is NULL or not. > No need to have this extra bit. Again, there may be some filesystems > that are a bit wonky here, but I'm sure they're fixable. > > 3. PG_mappedtodisk. This is really only used by the buffer cache. > Once the filesystems that use bufferheads have been converted, this can > go away. Nowadays (upstream) PG_anon_exclusive for anonymous memory. -- Thanks, David / dhildenb