From: Michel Lespinasse <walken@google.com>
To: Chinwen Chang <chinwen.chang@mediatek.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
Daniel Jordan <daniel.m.jordan@oracle.com>,
Davidlohr Bueso <dbueso@suse.de>,
Alexey Dobriyan <adobriyan@gmail.com>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
Jason Gunthorpe <jgg@ziepe.ca>,
Steven Price <steven.price@arm.com>,
Song Liu <songliubraving@fb.com>,
Jimmy Assarsson <jimmyassarsson@gmail.com>,
Huang Ying <ying.huang@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-arm-kernel@lists.infradead.org,
linux-mediatek@lists.infradead.org,
linux-fsdevel@vger.kernel.org, wsd_upstream@mediatek.com
Subject: Re: [PATCH v2 2/2] mm: proc: smaps_rollup: do not stall write attempts on mmap_lock
Date: Fri, 14 Aug 2020 01:35:37 -0700 [thread overview]
Message-ID: <CANN689FtCsC71cjAjs0GPspOhgo_HRj+diWsoU1wr98YPktgWg@mail.gmail.com> (raw)
In-Reply-To: <1597284810-17454-3-git-send-email-chinwen.chang@mediatek.com>
On Wed, Aug 12, 2020 at 7:13 PM Chinwen Chang
<chinwen.chang@mediatek.com> wrote:
> smaps_rollup will try to grab mmap_lock and go through the whole vma
> list until it finishes the iterating. When encountering large processes,
> the mmap_lock will be held for a longer time, which may block other
> write requests like mmap and munmap from progressing smoothly.
>
> There are upcoming mmap_lock optimizations like range-based locks, but
> the lock applied to smaps_rollup would be the coarse type, which doesn't
> avoid the occurrence of unpleasant contention.
>
> To solve aforementioned issue, we add a check which detects whether
> anyone wants to grab mmap_lock for write attempts.
I think your retry mechanism still doesn't handle all cases. When you
get back the mmap lock, the address where you stopped last time could
now be in the middle of a vma. I think the consistent thing to do in
that case would be to retry scanning from the address you stopped at,
even if it's not on a vma boundary anymore. You may have to change
smap_gather_stats to support that, though.
next prev parent reply other threads:[~2020-08-14 8:35 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-13 2:13 [PATCH v2 0/2] Try to release mmap_lock temporarily in smaps_rollup Chinwen Chang
2020-08-13 2:13 ` [PATCH v2 1/2] mmap locking API: add mmap_lock_is_contended() Chinwen Chang
2020-08-13 8:21 ` Steven Price
2020-08-14 8:30 ` Michel Lespinasse
2020-08-13 2:13 ` [PATCH v2 2/2] mm: proc: smaps_rollup: do not stall write attempts on mmap_lock Chinwen Chang
2020-08-13 8:21 ` Steven Price
2020-08-14 8:35 ` Michel Lespinasse [this message]
2020-08-14 9:08 ` Chinwen Chang
2020-08-13 9:53 ` [PATCH v2 0/2] Try to release mmap_lock temporarily in smaps_rollup Michel Lespinasse
2020-08-13 16:11 ` Chinwen Chang
2020-08-14 8:29 ` Michel Lespinasse
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