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Tue, 27 Apr 2021 20:05:44 -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> <20210427112527.GX235567@casper.infradead.org> In-Reply-To: <20210427112527.GX235567@casper.infradead.org> From: Xiongwei Song Date: Wed, 28 Apr 2021 11:05:18 +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: rspam01 X-Rspamd-Queue-Id: 2C827F2 X-Stat-Signature: e1z35yazf1po5feh4i8x8jcdmw8bjz8z Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf12; identity=mailfrom; envelope-from=""; helo=mail-lj1-f172.google.com; client-ip=209.85.208.172 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1619579135-414741 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 27, 2021 at 7:26 PM Matthew Wilcox wrote: > > On Tue, Apr 27, 2021 at 01:30:48PM +0800, Xiongwei Song wrote: > > 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 > > Yes, I understood that. What I don't understand is why appending the > __GFP_COMP to the trace would have been less confusing for you. > > Suppose I have some code which calls: > > kmalloc(10 * 1024, GFP_ATOMIC|__GFP_NOWARN|__GFP_NOMEMALLOC); > > and I see in my logs > > 0.08% call_site=ffffffff851d0cb0 ptr=0xffff8c04a4ca0000 bytes_req=10176 bytes_alloc=16384 gfp_flags=GFP_ATOMIC|__GFP_NOWARN|__GFP_NOMEMALLOC|__GFP_COMP > > That seems to me _more_ confusing because I would wonder "Where did that > __GFP_COMP come from?" Thank you for the comments. But I disagree. When I use trace, I hope I can get the precise data rather than something changed that I don't know , then I can get the correct conclusion or direction on my issue. Here my question is what the trace events are for if they don't provide the real situation? I think that's not graceful and friendly. >From my perspective, it'd be better to know my flags changed before checking code lines one by one. In other words, I need a warning to reminder me on this, then I can know quickly my process might do some incorrect things. Regards, Xiongwei