Re: [PATCH 04/10] xfs: split xfs_mod_freecounter

[Christoph Hellwig <hch@lst.de>]

On Fri, Feb 23, 2024 at 09:09:53AM -0800, Darrick J. Wong wrote:
> > -	lcounter = (long long)mp->m_resblks_avail + delta;
> > -	if (lcounter >= 0) {
> > -		mp->m_resblks_avail = lcounter;
> > +		xfs_warn_once(mp,
> > +"Reserve blocks depleted! Consider increasing reserve pool size.");
> 
> Hmm.  This message gets logged if the __percpu_counter_compare above
> returns a negative value and we don't have a reserve pool.  I think
> that's a change from the current code, where running out of m_frextents
> returns ENOSPC without generating (misleading) log messages about the
> reserve pool.

Yes, I'll need to fix that up.

> without all the reserve pool machinery that fdblocks has.  The original
> code to implement m_frextents did exactly that, but Dave really wanted
> me to optimize this for icache footprint[1] so we ended up with (IMO)
> harder to understand xfs_mod_freecounter.

FYI, I have uses for reserved frextents a bit down the road, so
I'll make use of that.  Without that splitting them would seem nicer
to me.