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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.

  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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