Re: [PATCH] btrfs: also add stripe entries for NOCOW writes

[Qu Wenruo]

在 2024/9/23 17:10, Johannes Thumshirn 写道:
> On 23.09.24 09:28, Qu Wenruo wrote:
> > 在 2024/9/23 16:15, Johannes Thumshirn 写道:
> > > From: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
> > >
> > > NOCOW writes do not generate stripe_extent entries in the RAID stripe
> > > tree, as the RAID stripe-tree feature initially was designed with a
> > > zoned filesystem in mind and on a zoned filesystem, we do not allow NOCOW
> > > writes. But the RAID stripe-tree feature is independent from the zoned
> > > feature, so we must also allow NOCOW writes for zoned filesystems.
> > >
> > > Signed-off-by: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
> >
> > Sorry I'm going to repeat myself again, I still believe if we insert an
> > RST entry at falloc() time, it will be more consistent with the non-RST
> > code.
> >
> > Yes, I known preallocated space will not need any read nor search RST
> > entry, and we just fill the page cache with zero at read time.
> >
> > But the point of proper (not just dummy) RST entry for the whole
> > preallocated space is, we do not need to touch the RST entry anymore for
> > NOCOW/PREALLOCATED write at all.
> >
> > This makes the RST NOCOW/PREALLOC writes behavior to align with the
> > non-RST code, which doesn't update any extent item, but only modify the
> > file extent for PREALLOC writes.
>
> Please re-read the patch. This is not a dummy RST entry but a real RST
> entry for NOCOW writes.
I know, but my point is, if the RST entry for preallocated range is
already a regular one, you won't even need to insert/update the RST tree
at all.

Just like we do not need to update the extent tree for
NOCOW/PREALLOCATED writes.

Thanks,
Qu