Re: [PATCH] Revert "btrfs: compression: don't try to compress if we don't have enough pages"

[David Sterba <dsterba@suse.cz>]

On Wed, Aug 25, 2021 at 08:06:57PM +0800, Qu Wenruo wrote:
> On 2021/8/25 下午7:55, David Sterba wrote:
> > On Wed, Aug 25, 2021 at 01:41:42PM +0800, Qu Wenruo wrote:
> >> This reverts commit f2165627319ffd33a6217275e5690b1ab5c45763.
> > 
> > At this point the revert is the simplest way to restore the inline
> > extent compression so that's what I'll probably do. However.
> >>
> >> [BUG]
> >> It's no longer possible to create compressed inline extent after commit
> >> f2165627319f ("btrfs: compression: don't try to compress if we don't
> >> have enough pages").
> >>
> >> [CAUSE]
> >> For compression code, there are several possible reasons we have a range
> >> that needs to be compressed while it's no more than one page.
> >>
> >> - Compressed inline write
> >>    The data is always smaller than one sector.
> > 
> > The missing logic was for the true inline extent. The patch was supposed
> > to skip compression for single pages other than inline extents, due to
> > efficiency. So I wonder if we want to do that or just don't bother as
> > it's probably a negligible amount of wasted time.
> 
> Yeah, I guess that's the case.
> 
> We may be able to do such check in the future, but at that time, we need 
> to take inline extents into consideration.
> 
> Thus it won't be just a simple @nr_pages check, but with extra 
> @start/@len check.

Yeah that's why revert is better than enhancing the test with the mising
bits.