public inbox for linux-um@lists.infradead.org
 help / color / mirror / Atom feed
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



_______________________________________________
linux-um mailing list
linux-um@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-um


      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]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=5868448.ctSSMDQgOm@blindfold \
    --to=richard@nod.at \
    --cc=anton.ivanov@cambridgegreys.com \
    --cc=axboe@kernel.dk \
    --cc=hch@lst.de \
    --cc=linux-um@lists.infradead.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox