From: Minchan Kim <minchan@kernel.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: zhong jiang <zhongjiang@huawei.com>,
akpm@linux-foundation.org, hannes@cmpxchg.org,
ktkhai@virtuozzo.com, linux-mm@kvack.org
Subject: Re: [PATCH] mm: fix unevictable page reclaim when calling madvise_pageout
Date: Wed, 30 Oct 2019 11:42:10 -0700 [thread overview]
Message-ID: <20191030184210.GB57267@google.com> (raw)
In-Reply-To: <20191030174533.GL31513@dhcp22.suse.cz>
On Wed, Oct 30, 2019 at 06:45:33PM +0100, Michal Hocko wrote:
> On Wed 30-10-19 09:52:39, Minchan Kim wrote:
> > On Tue, Oct 29, 2019 at 06:45:12PM +0800, zhong jiang wrote:
> > > On 2019/10/29 17:40, Michal Hocko wrote:
> > > > On Tue 29-10-19 17:30:57, zhong jiang wrote:
> > > >> On 2019/10/29 16:11, Michal Hocko wrote:
> > > >>> [Cc Minchan]
> > > > [...]
> > > >>> Removing a long existing BUG_ON begs for a much better explanation.
> > > >>> shrink_page_list is not a trivial piece of code but I _suspect_ that
> > > >>> removing it should be ok for mapped pages at least (try_to_unmap) but I
> > > >>> am not so sure how unmapped unevictable pages are handled from top of my
> > > >>> head.
> > > >> As to the unmapped unevictable pages. shrink_page_list has taken that into account.
> > > >>
> > > >> shinkr_page_list
> > > >> page_evictable --> will filter the unevictable pages to putback its lru.
> > > > Ohh, it is right there at the top. Missed it. The check has been added
> > > > by Nick along with the BUG_ON. So it is sounds more like a "this
> > > > shouldn't happen" bugon. I wouldn't mind to remove it with that
> > > > justification.
> > > As you has said, Minchan fix the same kind of bug by checking PageUnevictable (I did not notice before)
> > > Wait for Minchan to see whether he has better reason. thanks,
> >
> > madvise_pageout could work with a shared page and one of the vmas among processes
> > could do mlock so it could pass Unevictable LRU pages into shrink_page_list.
> > It's pointless to try reclaim unevictable pages from the beginning so I want to fix
> > madvise_pageout via introducing only_evictable flag into the API so that
> > madvise_pageout uses it as "true".
> >
> > If we want to remove the PageUnevictable VM_BUG_ON_PAGE in shrink_page_list,
> > I want to see more strong reason why it happens and why caller couldn't
> > filter them out from the beginning.
>
> Why is this preferable over removing the VM_BUG_ON condition? In other
> words why should we keep PageUnevictable check there?
I don't think it's reasonable to pass unevictalbe LRU pages into shrink_page_list
so wanted to know what race is here what we are missing to remove the BUG_ON
since mlock is heavily complicated.
>
> --
> Michal Hocko
> SUSE Labs
next prev parent reply other threads:[~2019-10-30 18:42 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-28 15:08 [PATCH] mm: fix unevictable page reclaim when calling madvise_pageout zhong jiang
2019-10-28 15:27 ` David Hildenbrand
2019-10-28 15:45 ` zhong jiang
2019-10-28 16:07 ` David Hildenbrand
2019-10-28 16:15 ` zhong jiang
2019-10-28 16:15 ` David Hildenbrand
2019-10-29 2:29 ` zhong jiang
2019-10-29 8:11 ` Michal Hocko
2019-10-29 9:30 ` zhong jiang
2019-10-29 9:40 ` Michal Hocko
2019-10-29 10:45 ` zhong jiang
2019-10-30 16:52 ` Minchan Kim
2019-10-30 17:22 ` Johannes Weiner
2019-10-30 18:39 ` Minchan Kim
2019-11-01 8:57 ` zhong jiang
2019-10-30 17:45 ` Michal Hocko
2019-10-30 18:42 ` Minchan Kim [this message]
2019-10-30 19:33 ` Johannes Weiner
2019-10-31 9:16 ` Michal Hocko
2019-10-31 14:48 ` Minchan Kim
2019-10-31 17:17 ` Michal Hocko
2019-11-01 12:56 ` zhong jiang
2019-10-31 9:46 ` zhong jiang
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