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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 615CEC433F5 for ; Wed, 10 Nov 2021 13:42:38 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E9EE0611AD for ; Wed, 10 Nov 2021 13:42:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org E9EE0611AD Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 6C1DC6B0072; Wed, 10 Nov 2021 08:42:37 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 671826B0073; Wed, 10 Nov 2021 08:42:37 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5602A6B0074; Wed, 10 Nov 2021 08:42:37 -0500 (EST) 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 47C936B0072 for ; Wed, 10 Nov 2021 08:42:37 -0500 (EST) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id EFB018008D for ; Wed, 10 Nov 2021 13:42:36 +0000 (UTC) X-FDA: 78793135512.17.618182B Received: from mail-io1-f41.google.com (mail-io1-f41.google.com [209.85.166.41]) by imf05.hostedemail.com (Postfix) with ESMTP id A21AE508EC91 for ; Wed, 10 Nov 2021 13:42:15 +0000 (UTC) Received: by mail-io1-f41.google.com with SMTP id z26so2783163iod.10 for ; Wed, 10 Nov 2021 05:42:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=v9i7u88nxI1XBqu3jYzX2JrdceQtSyBwNJT6G9SZhlY=; b=Qhx7Lyhvm+zRU1KsuMiRU/K7+wVtKexGEM6FqHCHpi2ug/HL0UZzdQNY0cbr91720k szZYTkUuZJ3zzq0sV690/b+UohoWPm0PS1XBkDSTAmatpJTvkOIK9Ee7l/9SfIjP+b5F MbJb/4YpfSpQclGpuiTDbSHLQqLXFwfYOeV67b1tSNIwgrLa53r3xYQ+byWgmOq34QHa 6LC5H/e1BMUVr5oja4ZFEpcca9UmZ9azybGDfWLNG01I4zrP5ZoKLkPFK5qh+k13X9KM 3pNLCFFopYWoR0AQ9GKAKHT0IFDA4sRQMZH0PU2OYVh9zLvwaEf68vkxvbIWsZLQW7tX geDA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=v9i7u88nxI1XBqu3jYzX2JrdceQtSyBwNJT6G9SZhlY=; b=Lch+FYFe4Fr3+wrWYt/yhqD9wNHgaG3FjsBkfTi/TeSBSjMb67y9zu5a3oS0A77J/N FqtOEBMIPBP/kQOE26aC1tXa15ZeLNVAn4b9QuJOmzXz3991a/O1wg2bjh5eeo0OUZak NM1NLjrUA0hzE6w3mBlboFF4PzajFYpd9TBEyiSs0tec2A26ajwJHHF8lKW8II5BbYhq d4xaU9/CGXS3hrTPfEnNNjJz3IED7Ce15QlNfF0HJUUntSBjvUPiTFbBVlEtAVNnUJQT oFJobCca9sqMByz3eQMQXI3XNStcSOWT4amPCz5leyArrQ4jZuYFoOQZXa1XAw587cuv 0frQ== X-Gm-Message-State: AOAM533h/smLcVbAPziF/t0TaOCqlPCbps/W9zTyU5g3qBx/La5nDG1Y h89nmQj/b7RO90PxPNmSEQr++TtlH7s7gl3oHFI= X-Google-Smtp-Source: ABdhPJx8k0gWxSHX2f9sM/iHyLVbZZnH8tCuIN3ZB89nv3YUII+HAv/a3VxYAYdcVzyV+qipzghbdpg2BB8CJFpazlM= X-Received: by 2002:a05:6638:4087:: with SMTP id m7mr403703jam.112.1636551755951; Wed, 10 Nov 2021 05:42:35 -0800 (PST) MIME-Version: 1.0 References: <20211110114721.133808-1-alexs@kernel.org> <20211110124034.2574-1-sj@kernel.org> In-Reply-To: <20211110124034.2574-1-sj@kernel.org> From: Alex Shi Date: Wed, 10 Nov 2021 21:41:59 +0800 Message-ID: Subject: Re: [RFC PATCH] mm/damon: remove damon_lock To: SeongJae Park Cc: Alex Shi , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: A21AE508EC91 X-Stat-Signature: 1iihb61ek6i16n4usbqopq3dc7fxbxep Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=Qhx7Lyhv; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf05.hostedemail.com: domain of seakeel@gmail.com designates 209.85.166.41 as permitted sender) smtp.mailfrom=seakeel@gmail.com X-HE-Tag: 1636551735-620140 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 Wed, Nov 10, 2021 at 8:40 PM SeongJae Park wrote: > > Thank you for this patch, Alex! > > On Wed, 10 Nov 2021 19:47:21 +0800 alexs@kernel.org wrote: > > > From: Alex Shi > > > > Variable nr_running_ctxs guards by damon_lock, but a lock for a int > > variable seems a bit heavy, a atomic_t is enough. > > The lock is not only for protecting nr_running_ctxs, but also for avoiding > different users concurrently executing damon_start(), because that could allow > the users interfering others. That's right. but it could be resolved by atomic too. like the following. > > > > > Signed-off-by: Alex Shi > > Cc: SeongJae Park > > Cc: Andrew Morton > > Cc: linux-mm@kvack.org > > Cc: linux-kernel@vger.kernel.org > > --- > > include/linux/damon.h | 1 - > > mm/damon/core.c | 31 +++++-------------------------- > > mm/damon/dbgfs.c | 8 +++++--- > > 3 files changed, 10 insertions(+), 30 deletions(-) > > > > diff --git a/include/linux/damon.h b/include/linux/damon.h > > index b4d4be3cc987..e5dcc6336ef2 100644 > > --- a/include/linux/damon.h > > +++ b/include/linux/damon.h > > @@ -453,7 +453,6 @@ int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int, > > unsigned long min_nr_reg, unsigned long max_nr_reg); > > int damon_set_schemes(struct damon_ctx *ctx, > > struct damos **schemes, ssize_t nr_schemes); > > -int damon_nr_running_ctxs(void); > > > > int damon_start(struct damon_ctx **ctxs, int nr_ctxs); > > int damon_stop(struct damon_ctx **ctxs, int nr_ctxs); > > diff --git a/mm/damon/core.c b/mm/damon/core.c > > index c381b3c525d0..e821e36d5c10 100644 > > --- a/mm/damon/core.c > > +++ b/mm/damon/core.c > [...] > > @@ -437,19 +422,15 @@ int damon_start(struct damon_ctx **ctxs, int nr_ctxs) > > int i; > > int err = 0; > > > > - mutex_lock(&damon_lock); > > - if (nr_running_ctxs) { > > - mutex_unlock(&damon_lock); > > + if (atomic_read(&nr_running_ctxs)) if (atomic_inc_not_zero(&nr_running_ctxs)) > > return -EBUSY; > > - } > > > > for (i = 0; i < nr_ctxs; i++) { > > err = __damon_start(ctxs[i]); > > if (err) > > break; > > - nr_running_ctxs++; > > + atomic_inc(&nr_running_ctxs); > > } > > - mutex_unlock(&damon_lock); > > atomic_dec(&nr_running_ctxs); Is it save the multiple ctxs issue? Thanks > > return err; > > } > > This would let multiple concurrent threads seeing nr_running_ctxs of zero and > therefore proceed together. > > > Thanks, > SJ