Re: [RFC PATCH 2/2] xfs: map KM_MAYFAIL to __GFP_RETRY_HARD
From: Dave Chinner <david@fromorbit.com>
Date: 2016-06-16 00:27:12
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On Mon, Jun 06, 2016 at 01:32:16PM +0200, Michal Hocko wrote:
quoted hunk ↗ jump to hunk
From: Michal Hocko <mhocko@suse.com> KM_MAYFAIL didn't have any suitable GFP_FOO counterpart until recently so it relied on the default page allocator behavior for the given set of flags. This means that small allocations actually never failed. Now that we have __GFP_RETRY_HARD flags which works independently on the allocation request size we can map KM_MAYFAIL to it. The allocator will try as hard as it can to fulfill the request but fails eventually if the progress cannot be made. Signed-off-by: Michal Hocko <mhocko@suse.com> --- fs/xfs/kmem.h | 3 +++ 1 file changed, 3 insertions(+)diff --git a/fs/xfs/kmem.h b/fs/xfs/kmem.h index 689f746224e7..34e6b062ce0e 100644 --- a/fs/xfs/kmem.h +++ b/fs/xfs/kmem.h@@ -54,6 +54,9 @@ kmem_flags_convert(xfs_km_flags_t flags) lflags &= ~__GFP_FS; } + if (flags & KM_MAYFAIL) + lflags |= __GFP_RETRY_HARD; +
I don't understand. KM_MAYFAIL means "caller handles allocation failure, so retry on failure is not required." To then map KM_MAYFAIL to a flag that implies the allocation will internally retry to try exceptionally hard to prevent failure seems wrong. IOWs, KM_MAYFAIL means XFS is just using for normal allocator behaviour here, so I'm not sure what problem this change is actually solving and it's not clear from the description.... Cheers, Dave. -- Dave Chinner david@fromorbit.com -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>