From: Baoquan He <bhe@redhat.com>
To: Hugh Dickins <hughd@google.com>, Michal Hocko <mhocko@kernel.org>,
Vlastimil Babka <vbabka@suse.cz>,
pifang@redhat.com
Cc: David Hildenbrand <david@redhat.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
akpm@linux-foundation.org, aarcange@redhat.com,
Mel Gorman <mgorman@suse.de>
Subject: Re: Memory hotplug softlock issue
Date: Tue, 20 Nov 2018 21:58:03 +0800 [thread overview]
Message-ID: <20181120135803.GA3369@MiWiFi-R3L-srv> (raw)
In-Reply-To: <3f1a82a8-f2aa-ac5e-e6a8-057256162321@suse.cz>
Hi,
On 11/20/18 at 02:38pm, Vlastimil Babka wrote:
> On 11/20/18 6:44 AM, Hugh Dickins wrote:
> > [PATCH] mm: put_and_wait_on_page_locked() while page is migrated
> >
> > We have all assumed that it is essential to hold a page reference while
> > waiting on a page lock: partly to guarantee that there is still a struct
> > page when MEMORY_HOTREMOVE is configured, but also to protect against
> > reuse of the struct page going to someone who then holds the page locked
> > indefinitely, when the waiter can reasonably expect timely unlocking.
> >
> > But in fact, so long as wait_on_page_bit_common() does the put_page(),
> > and is careful not to rely on struct page contents thereafter, there is
> > no need to hold a reference to the page while waiting on it. That does
>
> So there's still a moment where refcount is elevated, but hopefully
> short enough, right? Let's see if it survives Baoquan's stress testing.
Yes, I applied Hugh's patch 8 hours ago, then our QE Ping operated on
that machine, after many times of hot removing/adding, the endless
looping during mirgrating is not seen any more. The test result for
Hugh's patch is positive. I even suggested Ping increasing the memory
pressure to "stress -m 250", it still succeeded to offline and remove.
So I think this patch works to solve the issue. Thanks a lot for your
help, all of you.
High, will you post a formal patch in a separate thread?
Meanwhile we found sometime onlining page may not add back all memory
blocks on one memory board, then hot removing/adding them will cause
kernel panic. I will investigate further and collect information, see if
it's a kernel issue or udev issue.
Thanks
Baoquan
>
> > mean that this case cannot go back through the loop: but that's fine for
> > the page migration case, and even if used more widely, is limited by the
> > "Stop walking if it's locked" optimization in wake_page_function().
> >
> > Add interface put_and_wait_on_page_locked() to do this, using negative
> > value of the lock arg to wait_on_page_bit_common() to implement it.
> > No interruptible or killable variant needed yet, but they might follow:
> > I have a vague notion that reporting -EINTR should take precedence over
> > return from wait_on_page_bit_common() without knowing the page state,
> > so arrange it accordingly - but that may be nothing but pedantic.
> >
> > shrink_page_list()'s __ClearPageLocked(): that was a surprise! this
> > survived a lot of testing before that showed up. It does raise the
> > question: should is_page_cache_freeable() and __remove_mapping() now
> > treat a PG_waiters page as if an extra reference were held? Perhaps,
> > but I don't think it matters much, since shrink_page_list() already
> > had to win its trylock_page(), so waiters are not very common there: I
> > noticed no difference when trying the bigger change, and it's surely not
> > needed while put_and_wait_on_page_locked() is only for page migration.
> >
> > Signed-off-by: Hugh Dickins <hughd@google.com>
> > ---
>
> ...
>
> > @@ -1100,6 +1111,17 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
> > ret = -EINTR;
> > break;
> > }
> > +
> > + if (lock < 0) {
> > + /*
> > + * We can no longer safely access page->flags:
>
> Hmm...
>
> > + * even if CONFIG_MEMORY_HOTREMOVE is not enabled,
> > + * there is a risk of waiting forever on a page reused
> > + * for something that keeps it locked indefinitely.
> > + * But best check for -EINTR above before breaking.
> > + */
> > + break;
> > + }
> > }
> >
> > finish_wait(q, wait);
>
> ... the code continues by:
>
> if (thrashing) {
> if (!PageSwapBacked(page))
>
> So maybe we should not set 'thrashing' true when lock < 0?
>
> Thanks!
> Vlastimil
next prev parent reply other threads:[~2018-11-20 13:58 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-14 7:09 Memory hotplug softlock issue Baoquan He
2018-11-14 7:16 ` Baoquan He
2018-11-14 8:18 ` David Hildenbrand
2018-11-14 9:00 ` Baoquan He
2018-11-14 9:25 ` David Hildenbrand
2018-11-14 9:41 ` Michal Hocko
2018-11-14 9:48 ` David Hildenbrand
2018-11-14 10:04 ` Michal Hocko
2018-11-14 9:01 ` Michal Hocko
2018-11-14 9:22 ` David Hildenbrand
2018-11-14 9:37 ` Michal Hocko
2018-11-14 9:39 ` David Hildenbrand
2018-11-14 14:52 ` Baoquan He
2018-11-14 15:00 ` Michal Hocko
2018-11-15 5:10 ` Baoquan He
2018-11-15 7:30 ` Michal Hocko
2018-11-15 7:53 ` Baoquan He
2018-11-15 8:30 ` Michal Hocko
2018-11-15 9:42 ` David Hildenbrand
2018-11-15 9:52 ` Baoquan He
2018-11-15 9:53 ` David Hildenbrand
2018-11-15 13:12 ` Baoquan He
2018-11-15 13:19 ` Michal Hocko
2018-11-15 13:23 ` Baoquan He
2018-11-15 14:25 ` Michal Hocko
2018-11-15 13:38 ` Baoquan He
2018-11-15 14:32 ` Michal Hocko
2018-11-15 14:34 ` Baoquan He
2018-11-16 1:24 ` Baoquan He
2018-11-16 9:14 ` Michal Hocko
2018-11-17 4:22 ` Baoquan He
2018-11-19 10:52 ` Baoquan He
2018-11-19 12:40 ` Michal Hocko
2018-11-19 12:51 ` Michal Hocko
2018-11-19 14:10 ` Michal Hocko
2018-11-19 16:36 ` Vlastimil Babka
2018-11-19 16:46 ` Michal Hocko
2018-11-19 16:46 ` Vlastimil Babka
2018-11-19 16:48 ` Vlastimil Babka
2018-11-19 17:01 ` Michal Hocko
2018-11-19 17:33 ` Michal Hocko
2018-11-19 20:34 ` Hugh Dickins
2018-11-19 20:59 ` Michal Hocko
2018-11-20 1:56 ` Baoquan He
2018-11-20 5:44 ` Hugh Dickins
2018-11-20 13:38 ` Vlastimil Babka
2018-11-20 13:58 ` Baoquan He [this message]
2018-11-20 14:05 ` Michal Hocko
2018-11-20 14:12 ` Baoquan He
2018-11-21 1:21 ` Hugh Dickins
2018-11-21 1:08 ` Hugh Dickins
2018-11-21 3:20 ` Hugh Dickins
2018-11-21 17:31 ` Michal Hocko
2018-11-22 1:53 ` Hugh Dickins
2018-11-14 10:00 ` Michal Hocko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20181120135803.GA3369@MiWiFi-R3L-srv \
--to=bhe@redhat.com \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=david@redhat.com \
--cc=hughd@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mgorman@suse.de \
--cc=mhocko@kernel.org \
--cc=pifang@redhat.com \
--cc=vbabka@suse.cz \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).