[PATCH V2] XFS: fix zoned gc threshold math for 32-bit arches

[PATCH V2] XFS: fix zoned gc threshold math for 32-bit arches

[cem]

From: Carlos Maiolino <cem@kernel.org>

xfs_zoned_need_gc makes use of mult_frac() to calculate the threshold
for triggering the zoned garbage collector, but, turns out mult_frac()
doesn't properly work with 64-bit data types and this caused build
failures on some 32-bit architectures.

Fix this by essentially open coding mult_frac() in a 64-bit friendly
way.

Notice we don't need to bother with counters underflow here because
xfs_estimate_freecounter() will always return a positive value, as it
leverages percpu_counter_read_positive to read such counters.

Fixes: 845abeb1f06a ("xfs: add tunable threshold parameter for triggering zone GC")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202504181233.F7D9Atra-lkp@intel.com/
Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
---
V2:
	- threshold should be a s64, not s32

 fs/xfs/xfs_zone_gc.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_zone_gc.c b/fs/xfs/xfs_zone_gc.c
index 8c541ca71872..81c94dd1d596 100644
--- a/fs/xfs/xfs_zone_gc.c
+++ b/fs/xfs/xfs_zone_gc.c
@@ -170,7 +170,8 @@ bool
 xfs_zoned_need_gc(
 	struct xfs_mount	*mp)
 {
-	s64			available, free;
+	s64			available, free, threshold;
+	s32			remainder;
 
 	if (!xfs_group_marked(mp, XG_TYPE_RTG, XFS_RTG_RECLAIMABLE))
 		return false;
@@ -183,7 +184,12 @@ 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))
+
+	threshold = div_s64_rem(free, 100, &remainder);
+	threshold = threshold * mp->m_zonegc_low_space +
+		    remainder * div_s64(mp->m_zonegc_low_space, 100);
+
+	if (available < threshold)
 		return true;
 
 	return false;
-- 
2.49.0

Re: [PATCH V2] XFS: fix zoned gc threshold math for 32-bit arches

[Hans Holmberg]

On 22/04/2025 14:55, cem@kernel.org wrote:
> From: Carlos Maiolino <cem@kernel.org>
> 
> xfs_zoned_need_gc makes use of mult_frac() to calculate the threshold
> for triggering the zoned garbage collector, but, turns out mult_frac()
> doesn't properly work with 64-bit data types and this caused build
> failures on some 32-bit architectures.
> 
> Fix this by essentially open coding mult_frac() in a 64-bit friendly
> way.
> 
> Notice we don't need to bother with counters underflow here because
> xfs_estimate_freecounter() will always return a positive value, as it
> leverages percpu_counter_read_positive to read such counters.
> 
> Fixes: 845abeb1f06a ("xfs: add tunable threshold parameter for triggering zone GC")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202504181233.F7D9Atra-lkp@intel.com/
> Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
> ---
> V2:
> 	- threshold should be a s64, not s32
> 
>  fs/xfs/xfs_zone_gc.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_zone_gc.c b/fs/xfs/xfs_zone_gc.c
> index 8c541ca71872..81c94dd1d596 100644
> --- a/fs/xfs/xfs_zone_gc.c
> +++ b/fs/xfs/xfs_zone_gc.c
> @@ -170,7 +170,8 @@ bool
>  xfs_zoned_need_gc(
>  	struct xfs_mount	*mp)
>  {
> -	s64			available, free;
> +	s64			available, free, threshold;
> +	s32			remainder;
>  
>  	if (!xfs_group_marked(mp, XG_TYPE_RTG, XFS_RTG_RECLAIMABLE))
>  		return false;
> @@ -183,7 +184,12 @@ 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))
> +
> +	threshold = div_s64_rem(free, 100, &remainder);
> +	threshold = threshold * mp->m_zonegc_low_space +
> +		    remainder * div_s64(mp->m_zonegc_low_space, 100);
> +
> +	if (available < threshold)
>  		return true;
>  
>  	return false;


Thanks for fixing this up!

Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>

Re: [PATCH V2] XFS: fix zoned gc threshold math for 32-bit arches

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH V2] XFS: fix zoned gc threshold math for 32-bit arches

[Guenter Roeck]

On 4/22/25 05:54, cem@kernel.org wrote:
> From: Carlos Maiolino <cem@kernel.org>
> 
> xfs_zoned_need_gc makes use of mult_frac() to calculate the threshold
> for triggering the zoned garbage collector, but, turns out mult_frac()
> doesn't properly work with 64-bit data types and this caused build
> failures on some 32-bit architectures.
> 
> Fix this by essentially open coding mult_frac() in a 64-bit friendly
> way.
> 
> Notice we don't need to bother with counters underflow here because
> xfs_estimate_freecounter() will always return a positive value, as it
> leverages percpu_counter_read_positive to read such counters.
> 
> Fixes: 845abeb1f06a ("xfs: add tunable threshold parameter for triggering zone GC")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202504181233.F7D9Atra-lkp@intel.com/
> Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>

Succesfully built openrisc:allmodconfig and parisc:allmodconfig with gcc 13.3.

Tested-by: Guenter Roeck <linux@roeck-us.net>

Guenter

Re: [PATCH V2] XFS: fix zoned gc threshold math for 32-bit arches

[Carlos Maiolino]

On Tue, 22 Apr 2025 14:54:54 +0200, cem@kernel.org wrote:
> xfs_zoned_need_gc makes use of mult_frac() to calculate the threshold
> for triggering the zoned garbage collector, but, turns out mult_frac()
> doesn't properly work with 64-bit data types and this caused build
> failures on some 32-bit architectures.
> 
> Fix this by essentially open coding mult_frac() in a 64-bit friendly
> way.
> 
> [...]

Applied to for-next, thanks!

[1/1] XFS: fix zoned gc threshold math for 32-bit arches
      commit: bd7c19331913b955a7823e6315ca16bbcc65aeff

Best regards,
-- 
Carlos Maiolino <cem@kernel.org>