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From: Richard Weinberger <richard@nod.at>
To: Anton Ivanov <anton.ivanov@cambridgegreys.com>,
	linux-um@lists.infradead.org
Cc: Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] Add DISCARD support to UML udb driver
Date: Fri, 09 Nov 2018 23:06:00 +0100	[thread overview]
Message-ID: <5868448.ctSSMDQgOm@blindfold> (raw)
In-Reply-To: <79343bcf-8cf7-27e8-1d53-ee404f6431bd@cambridgegreys.com>

Am Freitag, 9. November 2018, 22:20:03 CET schrieb Anton Ivanov:
> > What shall happen if the host filesystem does not support these
> > fallocate() operations?
> > I guess we need to probe for them first and decide whether to
> > accept/offer the discard command
> > at run time.
> 
> If it the filesystem is using periodic (not realtime) fstrim, It will 
> return IO error on those and fstrim will fail. Normal file ops - write, 
> read, fsync should continue as this should not force a remount.
> 
> I could not test with realtime fstrim ans btrfs was having some issues 
> in 4.20-rc1. It was hitting spinlock recursions and irq on/off where 
> they should not be BUG()s.
> 
> Non-destructive probing is a bit difficult. IMHO, we should leave this 
> to the user and add flags the way nbd and loop have done it. We can also 
> add a config option to set a default on or off at compile time (same as 
> for sync io on ubd).

Well, we could do what qemu does.
If the syscall fails with -ENOTSUP, disable discard.

Thanks,
//richard



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      reply	other threads:[~2018-11-09 22:06 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-09  9:19 [PATCH] Add DISCARD support to UML udb driver anton.ivanov
2018-11-09 15:55 ` Jens Axboe
2018-11-09 21:04 ` Richard Weinberger
2018-11-09 21:20   ` Anton Ivanov
2018-11-09 22:06     ` Richard Weinberger [this message]

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