Date: Fri, 5 Oct 2012 19:02:24 +0300 From: Nikolay Denev <ndenev@gmail.com> To: Andriy Gapon <avg@freebsd.org> Cc: freebsd-fs <freebsd-fs@freebsd.org> Subject: Re: nfs + zfs hangs on RELENG_9 Message-ID: <7423226525986478629@unknownmsgid> In-Reply-To: <506ED16C.7000207@FreeBSD.org> References: <906543F2-96BD-4519-B693-FD5AFB646F87@gmail.com> <506BF372.1090208@FreeBSD.org> <CF9C7048-15C1-4C7A-8395-2BAB3AE31322@gmail.com> <506C4049.4040100@FreeBSD.org> <D50A4777-BF2E-438A-B15B-661D4CB3C3B6@gmail.com> <506D81A7.8030506@FreeBSD.org> <506DB5DB.7080302@FreeBSD.org> <506ED16C.7000207@FreeBSD.org>
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Applied and running. Will report if there are issues.
Sent from my iPhone
On 05.10.2012, at 15:24, Andriy Gapon <avg@freebsd.org> wrote:
> on 04/10/2012 19:14 Andriy Gapon said the following:
>> BTW, one thing to note here is that the lowmem hook was invoked because of KVA
>> space shortage, not because of page shortage.
>>
>> From practical point of view this may mean that having sufficient KVA size may
>> help to not run into this deadlock.
>>
>> From programming point of view I am tempted to let arc_lowmem block only if
>> curproc == pageproc. That should both handle the case where blocking is most
>> needed and should prevent the deadlock described above.
>
> A possible patch:
>
> --- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
> +++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
> @@ -3720,8 +3720,16 @@ arc_lowmem(void *arg __unused, int howto __unused)
> mutex_enter(&arc_reclaim_thr_lock);
> needfree = 1;
> cv_signal(&arc_reclaim_thr_cv);
> - while (needfree)
> - msleep(&needfree, &arc_reclaim_thr_lock, 0, "zfs:lowmem", 0);
> +
> + /*
> + * It is unsafe to block here in arbitrary threads, because we can come
> + * here from ARC itself and may hold ARC locks and thus risk a deadlock
> + * with ARC reclaim thread.
> + */
> + if (curproc == pageproc) {
> + while (needfree)
> + msleep(&needfree, &arc_reclaim_thr_lock, 0, "zfs:lowmem", 0);
> + }
> mutex_exit(&arc_reclaim_thr_lock);
> mutex_exit(&arc_lowmem_lock);
> }
>
> --
> Andriy Gapon
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