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Tue, 24 Mar 2020 10:11:15 +0000 (UTC) Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 A5CEC20775; Tue, 24 Mar 2020 10:11:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585044673; bh=qxQbFkvpQKNEY7WzNXo9Xl0byVovMYnxhwWOYOqVkLg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=x5cOK8jAB92LQpQluWsLS1p3JLzJvCG6JwPhclZD527G82OcEu+JPfrKMWHdLSBFf C/KP0L5Hys/rnaT0FMSUv9U8sl7Lk/lks4ezrpicMr9u4QtRIlTvyDMfsqk0dJIm2a lxaS4HL39yqfQTzGcRuvDAaKxQIZTwfZObSJsZ/k= Date: Tue, 24 Mar 2020 11:11:10 +0100 From: Greg KH To: Jaewon Kim Cc: leon@kernel.org, vbabka@suse.cz, adobriyan@gmail.com, akpm@linux-foundation.org, labbott@redhat.com, sumit.semwal@linaro.org, minchan@kernel.org, ngupta@vflare.org, sergey.senozhatsky.work@gmail.com, kasong@redhat.com, bhe@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, jaewon31.kim@gmail.com, linux-api@vger.kernel.org, kexec@lists.infradead.org Subject: Re: [RFC PATCH v2 1/3] meminfo_extra: introduce meminfo extra Message-ID: <20200324101110.GA2218981@kroah.com> References: <20200323080503.6224-1-jaewon31.kim@samsung.com> <20200323080503.6224-2-jaewon31.kim@samsung.com> <20200323095344.GB425358@kroah.com> <5E79CEB5.8070308@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <5E79CEB5.8070308@samsung.com> Content-Transfer-Encoding: quoted-printable 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, Mar 24, 2020 at 06:11:17PM +0900, Jaewon Kim wrote: > On 2020=EB=85=84 03=EC=9B=94 23=EC=9D=BC 18:53, Greg KH wrote: > >> +int register_meminfo_extra(atomic_long_t *val, int shift, const cha= r *name) > >> +{ > >> + struct meminfo_extra *meminfo, *memtemp; > >> + int len; > >> + int error =3D 0; > >> + > >> + meminfo =3D kzalloc(sizeof(*meminfo), GFP_KERNEL); > >> + if (!meminfo) { > >> + error =3D -ENOMEM; > >> + goto out; > >> + } > >> + > >> + meminfo->val =3D val; > >> + meminfo->shift_for_page =3D shift; > >> + strncpy(meminfo->name, name, NAME_SIZE); > >> + len =3D strlen(meminfo->name); > >> + meminfo->name[len] =3D ':'; > >> + strncpy(meminfo->name_pad, meminfo->name, NAME_BUF_SIZE); > >> + while (++len < NAME_BUF_SIZE - 1) > >> + meminfo->name_pad[len] =3D ' '; > >> + > >> + spin_lock(&meminfo_lock); > >> + list_for_each_entry_rcu(memtemp, &meminfo_head, list) { > >> + if (memtemp->val =3D=3D val) { > >> + error =3D -EINVAL; > >> + break; > >> + } > >> + } > >> + if (!error) > >> + list_add_tail_rcu(&meminfo->list, &meminfo_head); > >> + spin_unlock(&meminfo_lock); > > If you have a lock, why are you needing rcu? > I think _rcu should be removed out of list_for_each_entry_rcu. > But I'm confused about what you meant. > I used rcu_read_lock on __meminfo_extra, > and I think spin_lock is also needed for addition and deletion to handl= e multiple modifiers. If that's the case, then that's fine, it just didn't seem like that was needed. Or I might have been reading your rcu logic incorrectly... > >> + if (error) > >> + kfree(meminfo); > >> +out: > >> + > >> + return error; > >> +} > >> +EXPORT_SYMBOL(register_meminfo_extra); > > EXPORT_SYMBOL_GPL()? I have to ask :) > I can use EXPORT_SYMBOL_GPL. > > > > thanks, > > > > greg k-h > > > > >=20 > Hello > Thank you for your comment. >=20 > By the way there was not resolved discussion on v1 patch as I mentioned= on cover page. > I'd like to hear your opinion on this /proc/meminfo_extra node. I think it is the propagation of an old and obsolete interface that you will have to support for the next 20+ years and yet not actually be useful :) > Do you think this is meaningful or cannot co-exist with other future > sysfs based API. What sysfs-based API? I still don't know _why_ you want this. The ION stuff is not needed as that code is about to be deleted, so who else wants this? What is the use-case for it that is so desperately needed that parsing yet-another-proc file is going to solve the problem? thanks, greg k-h