From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4B859C4727D for ; Tue, 22 Sep 2020 16:51:20 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D2C7E22262 for ; Tue, 22 Sep 2020 16:51:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D2C7E22262 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 57838900025; Tue, 22 Sep 2020 12:51:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 528EA900003; Tue, 22 Sep 2020 12:51:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 43F10900025; Tue, 22 Sep 2020 12:51:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0075.hostedemail.com [216.40.44.75]) by kanga.kvack.org (Postfix) with ESMTP id 2DEC9900003 for ; Tue, 22 Sep 2020 12:51:19 -0400 (EDT) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id D50C81EE6 for ; Tue, 22 Sep 2020 16:51:18 +0000 (UTC) X-FDA: 77291287836.17.van66_341545b2714f Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin17.hostedemail.com (Postfix) with ESMTP id DE243180D0186 for ; Tue, 22 Sep 2020 16:51:17 +0000 (UTC) X-HE-Tag: van66_341545b2714f X-Filterd-Recvd-Size: 4297 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf33.hostedemail.com (Postfix) with ESMTP for ; Tue, 22 Sep 2020 16:51:17 +0000 (UTC) Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 23A9822262; Tue, 22 Sep 2020 16:51:15 +0000 (UTC) Date: Tue, 22 Sep 2020 12:51:13 -0400 From: Steven Rostedt To: Yafang Shao Cc: Axel Rasmussen , Ingo Molnar , Andrew Morton , Vlastimil Babka , Michel Lespinasse , Daniel Jordan , Davidlohr Bueso , LKML , Linux MM Subject: Re: [PATCH] mmap_lock: add tracepoints around lock acquisition Message-ID: <20200922125113.12ef1e03@gandalf.local.home> In-Reply-To: References: <20200917181347.1359365-1-axelrasmussen@google.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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, 22 Sep 2020 12:09:19 +0800 Yafang Shao wrote: > > > Are there any methods to avoid un-inlining these wrappers ? > > > > > > For example, > > > // include/linux/mmap_lock.h > > > > > > void mmap_lock_start_trace_wrapper(); > > > void mmap_lock_acquire_trace_wrapper(); > > > > > > static inline void mmap_write_lock(struct mm_struct *mm) > > > { > > > mmap_lock_start_trace_wrapper(); > > > down_write(&mm->mmap_lock); > > > mmap_lock_acquire_trace_wrapper(); > > > } > > > > > > // mm/mmap_lock.c > > > void mmap_lock_start_trace_wrapper() > > > { > > > trace_mmap_lock_start(); > > > } > > > > > > void mmap_lock_start_trace_wrapper() > > > { > > > trace_mmap_lock_acquired(); > > > } > > > > We can do something like that, but I don't think it would end up being better. > > > > At the end of the day, because the trace stuff cannot be in the > > header, we have to add an extra function call one way or the other. > > This would just move the call one step further down the call stack. > > So, I don't think it would affect performance in the > > CONFIG_MMAP_LOCK_STATS + tracepoints not enabled at runtime case. > > > > Right, it seems we have to add an extra function call. > > > Also the wrappers aren't quite so simple as this, they need some > > parameters to work. (the struct mm_struct, whether it was a read or a > > write lock, and whether or not the lock operation succeeded), so it > > would mean adding more inlined code, which I think adds up to be a > > nontrivial amount since these wrappers are called so often in the > > kernel. > > > > If you feel strongly, let me know and I can send a version as you > > describe and we can compare the two. > > > > These tracepoints will be less useful if we have to turn on the config > to enable it. > I don't mind implementing it that way if we can't optimize it. > > Maybe Steven can give some suggestions, Steven ? > What you can do, and what we have done is the following: (see include/linux/page_ref.h) #ifdef CONFIG_TRACING extern struct tracepoint __tracepoint_mmap_lock_start_locking; extern struct tracepoint __tracepoint_mmap_lock_acquire_returned; #define mmap_lock_tracepoint_active(t) static_key_false(&(__tracepoint_mmap_lock_##t).key) #else #define mmap_lock_tracepoint_active(t) false #endif static inline void mmap_write_lock(struct mm_struct *mm) { if (mmap_lock_tracepoint_active(start_locking)) mmap_lock_start_trace_wrapper(); down_write(&mm->mmap_lock); if (mmap_lock_tracepoint_active(acquire_returned)) mmap_lock_acquire_trace_wrapper(); } -- Steve