linux-kernel - Re: [PATCH] md: don't use flush_signals in userspace processes

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Date:   Fri, 9 Jun 2017 00:27:28 -0300
From:   Henrique de Moraes Holschuh <hmh@....eng.br>
To:     NeilBrown <neilb@...e.com>
Cc:     Mikulas Patocka <mpatocka@...hat.com>,
        Shaohua Li <shli@...nel.org>, linux-raid@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] md: don't use flush_signals in userspace processes

On Fri, 09 Jun 2017, NeilBrown wrote:
> Or maybe it could be discarded - the md_check_recovery() thing.
> The idea was that if you alt-sysrq-K to kill all processes, md arrays
> would go into immediate-safe-mode where the metadata is marked clean
> immediately after writes finish, rather than waiting a few seconds.  The
> chance of having a clean array after shutdown is hopefully improved.
> 
> I've never actually used this though, and I doubt many people know about
> it.  And bitmaps make it fairly pointless.

Hmm, I have, although I had no idea this was why my arrays were getting
far less frazzled than expected...  It is really useful behavior, now
that I know it can do that.

If you can teach SysRq+S, and especially SysRq+U, to force all arrays
into safe-mode *after* they carried their current meanings
(sync/umount), that would be more useful though, and it would help a lot
of people to avoid dirty arrays without them even knowing why...

-- 
  Henrique Holschuh