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Message-ID: <20240902202323.GC26776@twin.jikos.cz>
Date: Mon, 2 Sep 2024 22:23:23 +0200
From: David Sterba <dsterba@...e.cz>
To: Luca Stefani <luca.stefani.ge1@...il.com>
Cc: dsterba@...e.cz, Qu Wenruo <quwenruo.btrfs@....com>,
Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: Split remaining space to discard in chunks
On Mon, Sep 02, 2024 at 10:17:37PM +0200, Luca Stefani wrote:
> > sector_t nr_sects, gfp_t gfp_mask, struct bio **biop)
> > {
> > struct bio *bio;
> >
> > while ((bio = blk_alloc_discard_bio(bdev, §or, &nr_sects,
> > gfp_mask)))
> > *biop = bio_chain_and_submit(*biop, bio);
> > return 0;
> > }
> >
> > This is basically just a loop, chopping the input range as needed. The
> > btrfs code does effectively the same, there's only the superblock,
> > progress accounting and error handling done.
> >
> > As the maximum size of a single discard request depends on a device we
> > don't need to artificially limit it because this would require more IO
> > requests and can be slower.
>
> Thanks for taking a look, this change was prompted after I've been
> seeing issues due to the discard kthread blocking an userspace process
> causing device not to suspend.
> https://lore.kernel.org/lkml/20240822164908.4957-1-luca.stefani.ge1@gmail.com/
> is the proposed solution, but Qu mentioned that there is another place
> where it could happen that I didn't cover, and I think what I change
> here (unless it's the wrong place) allows me to add the similar
> `btrfs_trim_interrupted` checks to stop.
>
> Please let me know if that makes sense to you, if that's the case I
> guess it would make sense to send the 2 patches together?
Yeah for inserting the cancellation points it would make sense to do the
chunking. I'd suggest to do the same logic like blk_alloc_discard_bio()
and use the block device discard request limit and not a fixed constant.
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