Messages in this thread | | | Date | Mon, 10 Aug 2020 11:55:00 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH] mm/memcg: remove useless check on page->mem_cgroup |
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On Wed 05-08-20 20:28:33, Alex Shi wrote: [...] > >From 2ca3e87fd3878ab729551682ad083a70f15bb3fc Mon Sep 17 00:00:00 2001 > From: Alex Shi <alex.shi@linux.alibaba.com> > Date: Sat, 1 Aug 2020 10:43:55 +0800 > Subject: [PATCH v3] mm/memcg: warning on !memcg after readahead page charged > > Since readahead page is charged on memcg too, in theory we don't have to > check this exception now. Before safely remove them all, add a warning > for the unexpected !memcg. > > Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com> > Cc: Johannes Weiner <hannes@cmpxchg.org> > Cc: Michal Hocko <mhocko@kernel.org> > Cc: Vladimir Davydov <vdavydov.dev@gmail.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: cgroups@vger.kernel.org > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org
Looks good to me. I am not familiar with the section tweaks but that should be ok.
Acked-by: Michal Hocko <mhocko@suse.com>
Once you collect more feedback, please send both patches so that they do not get lost in this thread.
Thanks!
> --- > include/linux/mmdebug.h | 13 +++++++++++++ > mm/memcontrol.c | 15 ++++++++------- > 2 files changed, 21 insertions(+), 7 deletions(-) > > diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h > index 2ad72d2c8cc5..4ed52879ce55 100644 > --- a/include/linux/mmdebug.h > +++ b/include/linux/mmdebug.h > @@ -37,6 +37,18 @@ > BUG(); \ > } \ > } while (0) > +#define VM_WARN_ON_ONCE_PAGE(cond, page) ({ \ > + static bool __section(.data.once) __warned; \ > + int __ret_warn_once = !!(cond); \ > + \ > + if (unlikely(__ret_warn_once && !__warned)) { \ > + dump_page(page, "VM_WARN_ON_ONCE_PAGE(" __stringify(cond)")");\ > + __warned = true; \ > + WARN_ON(1); \ > + } \ > + unlikely(__ret_warn_once); \ > +}) > + > #define VM_WARN_ON(cond) (void)WARN_ON(cond) > #define VM_WARN_ON_ONCE(cond) (void)WARN_ON_ONCE(cond) > #define VM_WARN_ONCE(cond, format...) (void)WARN_ONCE(cond, format) > @@ -48,6 +60,7 @@ > #define VM_BUG_ON_MM(cond, mm) VM_BUG_ON(cond) > #define VM_WARN_ON(cond) BUILD_BUG_ON_INVALID(cond) > #define VM_WARN_ON_ONCE(cond) BUILD_BUG_ON_INVALID(cond) > +#define VM_WARN_ON_ONCE_PAGE(cond, page) BUILD_BUG_ON_INVALID(cond) > #define VM_WARN_ONCE(cond, format...) BUILD_BUG_ON_INVALID(cond) > #define VM_WARN(cond, format...) BUILD_BUG_ON_INVALID(cond) > #endif > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 130093bdf74b..299382fc55a9 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1322,10 +1322,8 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgd > } > > memcg = page->mem_cgroup; > - /* > - * Swapcache readahead pages are added to the LRU - and > - * possibly migrated - before they are charged. > - */ > + /* Readahead page is charged too, to see if other page uncharged */ > + VM_WARN_ON_ONCE_PAGE(!memcg, page); > if (!memcg) > memcg = root_mem_cgroup; > > @@ -6906,8 +6904,9 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage) > if (newpage->mem_cgroup) > return; > > - /* Swapcache readahead pages can get replaced before being charged */ > memcg = oldpage->mem_cgroup; > + /* Readahead page is charged too, to see if other page uncharged */ > + VM_WARN_ON_ONCE_PAGE(!memcg, oldpage); > if (!memcg) > return; > > @@ -7104,7 +7103,8 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry) > > memcg = page->mem_cgroup; > > - /* Readahead page, never charged */ > + /* Readahead page is charged too, to see if other page uncharged */ > + VM_WARN_ON_ONCE_PAGE(!memcg, page); > if (!memcg) > return; > > @@ -7168,7 +7168,8 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry) > > memcg = page->mem_cgroup; > > - /* Readahead page, never charged */ > + /* Readahead page is charged too, to see if other page uncharged */ > + VM_WARN_ON_ONCE_PAGE(!memcg, page); > if (!memcg) > return 0; > > -- > 1.8.3.1
-- Michal Hocko SUSE Labs
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