linux-kernel - Re: [PATCH] xfs: add tunable threshold parameter for triggering zone GC

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Message-ID: <bntghvwinsfah4xq2r5yqmpemgs6hqyilascl4zwnh2vm6og2c@fcaypngp64cy>
Date: Mon, 21 Apr 2025 10:08:23 +0200
From: Carlos Maiolino <cem@...nel.org>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Hans Holmberg <Hans.Holmberg@....com>, 
	Dave Chinner <david@...morbit.com>, "Darrick J . Wong" <djwong@...nel.org>, hch <hch@....de>, 
	"linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xfs: add tunable threshold parameter for triggering zone
 GC

On Sun, Apr 20, 2025 at 12:13:34PM -0700, Guenter Roeck wrote:
> On 4/20/25 11:07, Carlos Maiolino wrote:
> ...
> >>
> >> diff --git a/fs/xfs/xfs_zone_gc.c b/fs/xfs/xfs_zone_gc.c
> >> index 8c541ca71872..6dde2a680e75 100644
> >> --- a/fs/xfs/xfs_zone_gc.c
> >> +++ b/fs/xfs/xfs_zone_gc.c
> >> @@ -170,7 +170,7 @@ bool
> >>    xfs_zoned_need_gc(
> >>           struct xfs_mount        *mp)
> >>    {
> >> -       s64                     available, free;
> >> +       u64                     available, free, rem;
> >>
> >>           if (!xfs_group_marked(mp, XG_TYPE_RTG, XFS_RTG_RECLAIMABLE))
> >>                   return false;
> >> @@ -183,7 +183,12 @@ xfs_zoned_need_gc(
> >>                   return true;
> >>
> >>           free = xfs_estimate_freecounter(mp, XC_FREE_RTEXTENTS);
> >> -       if (available < mult_frac(free, mp->m_zonegc_low_space, 100))
> >> +
> >> +       rem = do_div(free, 100);
> >> +       free = free * mp->m_zonegc_low_space +
> >> +               div_u64(rem * mp->m_zonegc_low_space, 100);
> >> +
> >> +       if (available < free)
> >>                   return true;
> >
> > You're essentially open coding mult_frac(), if we can get mult_frac() to work
> > on 64-bit too (or add a 64-bit version), that seems a better generic solution.
> >
> 
> Yes, I know. Problem is that getting more than one maintainer involved tends to make
> it exponentially more difficult to get anything accepted. With that in mind, I prefer
> open coded solutions like the one I suggested above. A generic solution is then still
> possible, but it is disconnected from solving the immediate problem.
> 

I think this is fair for the moment, unless Hans/Christoph have a better idea?!

> Guenter
>