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bh=3pT3Vmr4qXyIpvaJ20iy54B0P7FiMhelVXGMDaZ+8vs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SpNmlEarS5VXMhH5cPPiEI3NT/7vsQIZdwZmLIdouHPJcHHvuicpH+YfpyVZq+KS6 Hcdpq2e4uFuDlEGygs+RF4C682bDkX2zUtxVtnKiJ6dwSel677HuJcbBoHaJbh0rgl ZZNRe927mlo+jVxOFR638RDvHnz7qMUmpJpcRvuupL0C0yn0GTenZXZiIWCO4tNZ5I khBPouKGJhNIa9KDn32In+YpVpOkmhr1HiGAwibexKjT4S1Fogbe1z2lyzlH0KQkv4 LAvo7CuM3dKpWQNtnLzEeh+2/P4NmdJCEMl+BdszGQEJtkj0MbnHQlXUXwTB5rPnF0 Krj7xf+5KGc/A== From: SeongJae Park To: Matthew Wilcox Cc: Kefeng Wang , Andrew Morton , SeongJae Park , damon@lists.linux.dev, linux-mm@kvack.org, vishal.moola@gmail.com, david@redhat.com Subject: Re: [PATCH -next v3 2/7] mm/damon: introduce damon_get_folio() Date: Wed, 28 Dec 2022 23:14:17 +0000 Message-Id: <20221228231417.150148-1-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: B2CD84000A X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: 8tfzopuurxtmdk6nsjd6u1nitnzrygto X-HE-Tag: 1672269261-640775 X-HE-Meta: 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 vhnwMgp/ wBJqIsAbkRskLmn++cACzAlVv9kTH9oWmu5dDS2ohwB82DI75CpOeZrYXOdx9QzgUJ0GSs+1kEe1YDW4I6CYWyrJWWMLoNqhNEqzH9yBWXcJ9coBM0Ws9zT7rDep3Fcvzk6HwNUtzvgPl/FAwqJb26ROkzLQkmW6FAlPEUHiQZOcttzaMF0PbF7BFzO+8kT4dwcvO 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: Hi Matthew, On Wed, 28 Dec 2022 22:36:20 +0000 Matthew Wilcox wrote: > On Wed, Dec 28, 2022 at 07:34:08PM +0800, Kefeng Wang wrote: > > +static inline struct page *damon_get_page(unsigned long pfn) > > +{ > > + struct folio *folio = damon_get_folio(pfn); > > + > > + /* when folio is NULL, return &(0->page) mean return NULL */ > > + return &folio->page; > > I really don't think this comment is needed. This is the standard idiom > for converting from a folio to its head page. Well, I think some of DAMON code readers (at least me) might not yet that familiar with Folio, as it has not been a while since DAMON started using Folio. Also, maybe I overlooked some comments or documents, but I was unable to sure if the offset of 'page' in 'folio' is intended to be never changed with any future changes, or not. So I thought adding one more line of explanation here could be helpful for someone. I also show some code using 'folio_page(folio, 0)', so I might not be the only one who at least sometimes forget the idiom. For helping people remember this idiom easier, what do you think about having a new macro or static inline function, say, 'folio_head_page()' and comment why passing NULL is ok on the function? IMHO, that would be easier to read. Thanks, SJ