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Miller" , Eric Dumazet , Frederic Weisbecker , Jakub Kicinski , Joel Fernandes , Jonathan Corbet , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , Neeraj Upadhyay , Paolo Abeni , "Paul E. McKenney" Subject: Re: [PATCH 0/7] remove SLOB and allow kfree() with kmem_cache_alloc() Message-ID: References: <20230310103210.22372-1-vbabka@suse.cz> <20230313123147.6d28c47e@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230313123147.6d28c47e@gandalf.local.home> X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: 64z1x1xfxb3fgddnz6n75e8gyzocn9ax X-Rspamd-Queue-Id: 6A73A4001A X-HE-Tag: 1678730433-88266 X-HE-Meta: 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 kJkqCs9W 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 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 Mon, Mar 13, 2023 at 12:31:47PM -0400, Steven Rostedt wrote: > On Sun, 12 Mar 2023 11:51:29 +0200 > Mike Rapoport wrote: > > > git grep -in slob still gives a couple of matches. I've dropped the > > irrelevant ones it it left me with these: > > > > CREDITS:14:D: SLOB slab allocator > > kernel/trace/ring_buffer.c:358: * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing > > mm/Kconfig:251: SLOB allocator and is not recommended for systems with more than > > mm/Makefile:25:KCOV_INSTRUMENT_slob.o := n > > > > Except the comment in kernel/trace/ring_buffer.c all are trivial. > > > > As for the comment in ring_buffer.c, it looks completely irrelevant at this > > point. > > > > @Steve? > > You want me to remember something I wrote almost 15 years ago? I just wanted to make sure you don't have a problem with removing this comment :) > I think I understand that comment as much as you do. Yeah, that was when > I was still learning to write comments for my older self to understand, > and I failed miserably! > > But git history comes to the rescue. The commit that added that comment was: > > ed56829cb3195 ("ring_buffer: reset buffer page when freeing") > > This was at a time when it was suggested to me to use the struct page > directly in the ring buffer and where we could do fun "tricks" for > "performance". (I was never really for this, but I wasn't going to argue). > > And the code in question then had: > > /* > * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing > * this issue out. > */ > static inline void free_buffer_page(struct buffer_page *bpage) > { > reset_page_mapcount(&bpage->page); > bpage->page.mapping = NULL; > __free_page(&bpage->page); > } > > > But looking at commit: e4c2ce82ca27 ("ring_buffer: allocate buffer page > pointer") > > It was finally decided that method was not safe, and we should not be using > struct page but just allocate an actual page (much safer!). > > I never got rid of the comment, which was more about that > "reset_page_mapcount()", and should have been deleted back then. Yeah, I did the same analysis, just was too lazy to post it. > Just remove that comment. And you could even add: > > Suggested-by: Steven Rostedt (Google) > Fixes: e4c2ce82ca27 ("ring_buffer: allocate buffer page pointer") > > -- Steve -- Sincerely yours, Mike.