On Sun 17-09-17 10:45:34, Jerome Glisse wrote: > On Fri, Sep 15, 2017 at 09:01:00AM +0200, Michal Hocko wrote: > > On Thu 14-09-17 15:00:11, jglisse@xxxxxxxxxx wrote: > > > From: Jérôme Glisse <jglisse@xxxxxxxxxx> > > > > > > Fix for 4.14, zone device page always have an elevated refcount > > > of one and thus page count sanity check in uncharge_page() is > > > inappropriate for them. > > > > > > Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx> > > > Reported-by: Evgeny Baskakov <ebaskakov@xxxxxxxxxx> > > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > > > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > > > Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> > > > > Acked-by: Michal Hocko <mhocko@xxxxxxxx> > > > > Side note. Wouldn't it be better to re-organize the check a bit? It is > > true that this is VM_BUG so it is not usually compiled in but when it > > preferably checks for unlikely cases first while the ref count will be > > 0 in the prevailing cases. So can we have > > VM_BUG_ON_PAGE(page_count(page) && !is_zone_device_page(page) && > > !PageHWPoison(page), page); > > > > I would simply fold this nano optimization into the patch as you are > > touching it already. Not sure it is worth a separate commit. > > I am traveling sorry for late answer. This nano optimization make sense > Andrew do you want me to respin or should we leave it be ? I don't mind > either way. Andrew, could you fold this into the patch then? --- >From 73b5c07aed76aa68b413e708852da63ed9eb965c Mon Sep 17 00:00:00 2001 From: Michal Hocko <mhocko@xxxxxxxx> Date: Mon, 18 Sep 2017 08:27:43 +0200 Subject: [PATCH] memcg: nano-optimize VM_BUG_ON in uncharge_page Even though VM_BUG* is usually not compiled in there are systems which enable CONFIG_DEBUG_VM by default. VM_BUG_ON_PAGE in uncharge_page is not very optimal for the normal case. All pages should have counter==0 so that is the first thing to check. is_zone_device_page is nicely noop if ZONE_DEVICE is not compiled in and finally HW poison pages should be least probable. So reorder the check to bail out as early as possible on normal case. Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> --- mm/memcontrol.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index ae37b5624eb2..d5f3a62887cf 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5658,8 +5658,8 @@ static void uncharge_batch(const struct uncharge_gather *ug) static void uncharge_page(struct page *page, struct uncharge_gather *ug) { VM_BUG_ON_PAGE(PageLRU(page), page); - VM_BUG_ON_PAGE(!PageHWPoison(page) && !is_zone_device_page(page) && - page_count(page), page); + VM_BUG_ON_PAGE(page_count(page) && !is_zone_device_page(page) && + !PageHWPoison(page) , page); if (!page->mem_cgroup) return; -- 2.14.1 -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>