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Mon, 26 Apr 2021 22:31:15 -0700 (PDT) MIME-Version: 1.0 References: <1619491400-1904-1-git-send-email-sxwjean@me.com> <20210427025358.GV235567@casper.infradead.org> <20210427033632.GW235567@casper.infradead.org> In-Reply-To: From: Xiongwei Song Date: Tue, 27 Apr 2021 13:30:48 +0800 Message-ID: Subject: Re: [PATCH] mm: append __GFP_COMP flag for trace_malloc To: Matthew Wilcox Cc: Xiongwei Song , cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, vbabka@suse.cz, linux-mm@kvack.org, Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 58151E000129 X-Stat-Signature: f8kde34zf6dhn9wnhgzkbbh6gnz1myhf Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf30; identity=mailfrom; envelope-from=""; helo=mail-lf1-f52.google.com; client-ip=209.85.167.52 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1619501458-73211 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 Mattew, One more thing I should explain, the kmalloc_order() appends the __GFP_COMP flags, not by the caller. void *kmalloc_order(size_t size, gfp_t flags, unsigned int order) { ........................................................... flags |= __GFP_COMP; page = alloc_pages(flags, order); ........................................................... return ret; } EXPORT_SYMBOL(kmalloc_order); #ifdef CONFIG_TRACING void *kmalloc_order_trace(size_t size, gfp_t flags, unsigned int order) { void *ret = kmalloc_order(size, flags, order); trace_kmalloc(_RET_IP_, ret, size, PAGE_SIZE << order, flags); return ret; } EXPORT_SYMBOL(kmalloc_order_trace); #endif Regards, Xiongwei On Tue, Apr 27, 2021 at 12:11 PM Xiongwei Song wrote: > > On Tue, Apr 27, 2021 at 11:36 AM Matthew Wilcox wrote: > > > > On Tue, Apr 27, 2021 at 11:29:32AM +0800, Xiongwei Song wrote: > > > On Tue, Apr 27, 2021 at 10:54 AM Matthew Wilcox wrote: > > > > > > > > On Tue, Apr 27, 2021 at 10:43:20AM +0800, Xiongwei Song wrote: > > > > > From: Xiongwei Song > > > > > > > > > > When calling kmalloc_order, the flags should include __GFP_COMP here, > > > > > so that trace_malloc can trace the precise flags. > > > > > > > > I suppose that depends on your point of view. > > > Correct. > > > > > > Should we report the > > > > flags used by the caller, or the flags that we used to allocate memory? > > > > And why does it matter? > > > When I capture kmem:kmalloc events on my env with perf: > > > (perf record -p my_pid -e kmem:kmalloc) > > > I got the result below: > > > 0.08% call_site=ffffffff851d0cb0 ptr=0xffff8c04a4ca0000 > > > bytes_req=10176 bytes_alloc=16384 > > > gfp_flags=GFP_ATOMIC|__GFP_NOWARN|__GFP_NOMEMALLOC > > > > Hmm ... if you have a lot of allocations about this size, that would > > argue in favour of adding a kmem_cache of 10880 [*] bytes. That way, > > we'd get 3 allocations per 32kB instead of 2. > I understand you. But I don't think our process needs this size. This size > may be a bug in our code or somewhere, I don't know the RC for now. > > > [*] 32768 / 3, rounded down to a 64 byte cacheline > > > > But I don't understand why this confused you. Your caller at > > ffffffff851d0cb0 didn't specify __GFP_COMP. I'd be more confused if > > this did report __GFP_COMP. > > > I just wanted to save some time when debugging. > > Regards