From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx187.postini.com [74.125.245.187]) by kanga.kvack.org (Postfix) with SMTP id ECF9C6B0062 for ; Sat, 9 Jun 2012 11:55:48 -0400 (EDT) Received: from /spool/local by e28smtp04.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 9 Jun 2012 21:25:45 +0530 Received: from d28av03.in.ibm.com (d28av03.in.ibm.com [9.184.220.65]) by d28relay03.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q59FtgB511141564 for ; Sat, 9 Jun 2012 21:25:43 +0530 Received: from d28av03.in.ibm.com (loopback [127.0.0.1]) by d28av03.in.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q59LOw6Q029756 for ; Sun, 10 Jun 2012 07:24:58 +1000 From: "Aneesh Kumar K.V" Subject: Re: [PATCH -V8 14/16] hugetlb/cgroup: add charge/uncharge calls for HugeTLB alloc/free In-Reply-To: <20120609143054.GH1761@cmpxchg.org> References: <1339232401-14392-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1339232401-14392-15-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20120609092301.GF1761@cmpxchg.org> <87pq98ljil.fsf@skywalker.in.ibm.com> <20120609143054.GH1761@cmpxchg.org>User-Agent: Notmuch/0.11.1+346~g13d19c3 (http://notmuchmail.org) Emacs/23.3.1 (x86_64-pc-linux-gnu) Date: Sat, 09 Jun 2012 21:25:37 +0530 Message-ID: <87wr3gfpja.fsf@skywalker.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, dhillf@gmail.com, rientjes@google.com, mhocko@suse.cz, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Johannes Weiner writes: > On Sat, Jun 09, 2012 at 06:39:06PM +0530, Aneesh Kumar K.V wrote: >> Johannes Weiner writes: >> >> > On Sat, Jun 09, 2012 at 02:29:59PM +0530, Aneesh Kumar K.V wrote: >> >> From: "Aneesh Kumar K.V" >> >> >> >> This adds necessary charge/uncharge calls in the HugeTLB code. We do >> >> hugetlb cgroup charge in page alloc and uncharge in compound page destructor. >> >> >> >> Signed-off-by: Aneesh Kumar K.V >> >> --- >> >> mm/hugetlb.c | 16 +++++++++++++++- >> >> mm/hugetlb_cgroup.c | 7 +------ >> >> 2 files changed, 16 insertions(+), 7 deletions(-) >> >> >> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> >> index bf79131..4ca92a9 100644 >> >> --- a/mm/hugetlb.c >> >> +++ b/mm/hugetlb.c >> >> @@ -628,6 +628,8 @@ static void free_huge_page(struct page *page) >> >> BUG_ON(page_mapcount(page)); >> >> >> >> spin_lock(&hugetlb_lock); >> >> + hugetlb_cgroup_uncharge_page(hstate_index(h), >> >> + pages_per_huge_page(h), page); >> > >> > hugetlb_cgroup_uncharge_page() takes the hugetlb_lock, no? >> >> Yes, But this patch also modifies it to not take the lock, because we >> hold spin_lock just below in the call site. I didn't want to drop the >> lock and take it again. > > Sorry, I missed that. > >> > It's quite hard to review code that is split up like this. Please >> > always keep the introduction of new functions in the same patch that >> > adds the callsite(s). >> >> One of the reason I split the charge/uncharge routines and the callers >> in separate patches is to make it easier for review. Irrespective of >> the call site charge/uncharge routines should be correct with respect >> to locking and other details. What I did in this patch is a small >> optimization of avoiding dropping and taking the lock again. May be the >> right approach would have been to name it __hugetlb_cgroup_uncharge_page >> and make sure the hugetlb_cgroup_uncharge_page still takes spin_lock. >> But then we don't have any callers for that. > > I think this makes it needlessly complicated and there is no correct > or incorrect locking in (initially) dead code :-) > > The callsites are just a few lines. It's harder to review if you > introduce an API and then change it again mid-patchset. > I will fold the patches. > If there are no callers for a function that grabs the lock itself, > don't add it. Just add a note to the kerneldoc that explains the > requirement or put VM_BUG_ON(!spin_is_locked(&hugetlb_lock)); in > there or so. That is excellent. I will add kerneldoc and VM_BUG_ON. -aneesh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org