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

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Message-ID: <20250422114231.1012462-1-cem@kernel.org>
Date: Tue, 22 Apr 2025 13:42:23 +0200
From: cem@...nel.org
To: linux-xfs@...r.kernel.org
Cc: hch@....de,
	Hans.Holmberg@....com,
	linux@...ck-us.net,
	linux-kernel@...r.kernel.org,
	oe-kbuild-all@...ts.linux.dev
Subject: [PATCH] XFS: fix zoned gc threshold math for 32-bit arches

From: Carlos Maiolino <cem@...nel.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@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202504181233.F7D9Atra-lkp@intel.com/
Signed-off-by: Carlos Maiolino <cmaiolino@...hat.com>
---

 fs/xfs/xfs_zone_gc.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_zone_gc.c b/fs/xfs/xfs_zone_gc.c
index 8c541ca71872..b0e8915ef733 100644
--- a/fs/xfs/xfs_zone_gc.c
+++ b/fs/xfs/xfs_zone_gc.c
@@ -171,6 +171,7 @@ xfs_zoned_need_gc(
 	struct xfs_mount	*mp)
 {
 	s64			available, free;
+	s32			threshold, 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