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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1psPBm-004g8u-5V; Fri, 28 Apr 2023 14:35:10 +0000 Date: Fri, 28 Apr 2023 15:35:10 +0100 From: Matthew Wilcox To: Andrew Morton Cc: "zhaoyang.huang" , Minchan Kim , Joonsoo Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Zhaoyang Huang , ke.wang@unisoc.com Subject: Re: [PATCH] mm: fix printk format within cma Message-ID: References: <1681788789-19679-1-git-send-email-zhaoyang.huang@unisoc.com> <20230418123338.3b85a013cf6ce1fcb3677ae2@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230418123338.3b85a013cf6ce1fcb3677ae2@linux-foundation.org> X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: 4u3wyg1egph7657bi6x7yu3qbgqamc18 X-Rspamd-Queue-Id: 9F32C8000C X-HE-Tag: 1682692532-532243 X-HE-Meta: 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 LKNdgMy7 u5J+ZR424HA04F7yFhkPngDixmawwD6xn87gP5153pnTvfKp6hx0GiLSv/NFlw7/wXdljvOQ9HEhu3JARxK1B0iSrnJ47rrzUkHdNfS6p+ExU4XtA3Z/ajPkxrCvBXd8eK8qcanGVwoh82RBQYH9CR+lRw/+LLe6B+oDVL0iX2Ch9UapA2zMW1o53JJ3FSdAp93o8 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 Tue, Apr 18, 2023 at 12:33:38PM -0700, Andrew Morton wrote: > On Tue, 18 Apr 2023 04:38:24 +0100 Matthew Wilcox wrote: > > > On Tue, Apr 18, 2023 at 11:33:09AM +0800, zhaoyang.huang wrote: > > > cma and page pointer printed via %p are hash value which make debug to be hard. > > > change them to %px. > > > > Why does printing the page pointer make any sense at all? Surely the > > PFN makes much more sense. > > I suppose one could correlate a particular hashed pointer with other > debug output, see "ah, that's the same page". In which case one > doesn't really care whether or not the address is hashed - it's just a > cookie. This sounds thin. > > I doubt if a lot of thought went into the printk. If the page pointer > isn't useful then how about we simply remove it from the message? If something about it weren't useful, I don't think we'd be seeing a patch to transform it from a hashed pointer to an unhashed pointer? I'm pretty sure the PFN is the real information that's wanted here, since you can look at the hardware RAM layout to determine why that's not eligible.