From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Shi Subject: Re: [PATCH 18/18] mm: memcontrol: update page->mem_cgroup stability rules Date: Tue, 21 Apr 2020 17:20:59 +0800 Message-ID: <1f905391-5676-2db6-efb9-74ade130740e@linux.alibaba.com> References: <20200420221126.341272-1-hannes@cmpxchg.org> <20200420221126.341272-19-hannes@cmpxchg.org> Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20200420221126.341272-19-hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="iso-8859-1" To: Johannes Weiner , Joonsoo Kim Cc: Shakeel Butt , Hugh Dickins , Michal Hocko , "Kirill A. Shutemov" , Roman Gushchin , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kernel-team-b10kYP2dOMg@public.gmane.org =D4=DA 2020/4/21 =C9=CF=CE=E76:11, Johannes Weiner =D0=B4=B5=C0: > The previous patches have simplified the access rules around > page->mem_cgroup somewhat: >=20 > 1. We never change page->mem_cgroup while the page is isolated by > somebody else. This was by far the biggest exception to our rules > and it didn't stop at lock_page() or lock_page_memcg(). >=20 > 2. We charge pages before they get put into page tables now, so the > somewhat fishy rule about "can be in page table as long as it's > still locked" is now gone and boiled down to having an exclusive > reference to the page. >=20 > Document the new rules. Any of the following will stabilize the > page->mem_cgroup association: >=20 > - the page lock > - LRU isolation > - lock_page_memcg() > - exclusive access to the page >=20 > Signed-off-by: Johannes Weiner Reviewed-by: Alex Shi > --- > mm/memcontrol.c | 21 +++++++-------------- > 1 file changed, 7 insertions(+), 14 deletions(-) >=20 > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index a8cce52b6b4d..7b63260c9b57 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1201,9 +1201,8 @@ int mem_cgroup_scan_tasks(struct mem_cgroup *memcg, > * @page: the page > * @pgdat: pgdat of the page > * > - * This function is only safe when following the LRU page isolation > - * and putback protocol: the LRU lock must be held, and the page must > - * either be PageLRU() or the caller must have isolated/allocated it. > + * This function relies on page->mem_cgroup being stable - see the > + * access rules in commit_charge(). > */ > struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_d= ata *pgdat) > { > @@ -2605,18 +2604,12 @@ static void commit_charge(struct page *page, stru= ct mem_cgroup *memcg) > { > VM_BUG_ON_PAGE(page->mem_cgroup, page); > /* > - * Nobody should be changing or seriously looking at > - * page->mem_cgroup at this point: > - * > - * - the page is uncharged > - * > - * - the page is off-LRU > - * > - * - an anonymous fault has exclusive page access, except for > - * a locked page table > + * Any of the following ensures page->mem_cgroup stability: > * > - * - a page cache insertion, a swapin fault, or a migration > - * have the page locked > + * - the page lock > + * - LRU isolation > + * - lock_page_memcg() > + * - exclusive reference > */ > page->mem_cgroup =3D memcg; > } >=20