From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Aneesh Kumar K.V" Subject: Re: [PATCH -V8 12/16] hugetlb/cgroup: Add support for cgroup removal Date: Mon, 11 Jun 2012 21:04:43 +0530 Message-ID: <87bokpvp4c.fsf@skywalker.in.ibm.com> References: <1339232401-14392-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1339232401-14392-13-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20120611085258.GD12402@tiehlicka.suse.cz> <87fwa25gqj.fsf@skywalker.in.ibm.com> <20120611131411.GN12402@tiehlicka.suse.cz> Mime-Version: 1.0 Return-path: In-Reply-To: <20120611131411.GN12402@tiehlicka.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Michal Hocko Cc: linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, dhillf@gmail.com, rientjes@google.com, akpm@linux-foundation.org, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Michal Hocko writes: > On Mon 11-06-12 15:10:20, Aneesh Kumar K.V wrote: >> Michal Hocko writes: > [...] >> >> +static int hugetlb_cgroup_move_parent(int idx, struct cgroup *cgroup, >> >> + struct page *page) >> > >> > deserves a comment about the locking (needs to be called with >> > hugetlb_lock). >> >> will do >> >> > >> >> +{ >> >> + int csize; >> >> + struct res_counter *counter; >> >> + struct res_counter *fail_res; >> >> + struct hugetlb_cgroup *page_hcg; >> >> + struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_cgroup(cgroup); >> >> + struct hugetlb_cgroup *parent = parent_hugetlb_cgroup(cgroup); >> >> + >> >> + if (!get_page_unless_zero(page)) >> >> + goto out; >> >> + >> >> + page_hcg = hugetlb_cgroup_from_page(page); >> >> + /* >> >> + * We can have pages in active list without any cgroup >> >> + * ie, hugepage with less than 3 pages. We can safely >> >> + * ignore those pages. >> >> + */ >> >> + if (!page_hcg || page_hcg != h_cg) >> >> + goto err_out; >> > >> > How can we have page_hcg != NULL && page_hcg != h_cg? >> >> pages belonging to other cgroup ? > > OK, I've forgot that you are iterating over all active huge pages in > hugetlb_cgroup_pre_destroy. What prevents you from doing the filtering > in the caller? > I am also wondering why you need to play with the page reference > counting here. You are under hugetlb_lock so the page cannot disappear > in the meantime or am I missing something? That is correct. Updated the patch and also added the below comment to the function. + +/* + * Should be called with hugetlb_lock held. + * Since we are holding hugetlb_lock, pages cannot get moved from + * active list or uncharged from the cgroup, So no need to get + * page reference and test for page active here. + */ -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