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xfs: fall back to vmalloc when allocation log vector buffers

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When using large directory blocks, we regularly see memory
allocations of >64k being made for the shadow log vector buffer.
When we are under memory pressure, kmalloc() may not be able to find
contiguous memory chunks large enough to satisfy these allocations
easily, and if memory is fragmented we can potentially stall here.

TO avoid this problem, switch the log vector buffer allocation to
use kmem_alloc_large(). This will allow failed allocations to fall
back to vmalloc and so remove the dependency on large contiguous
regions of memory being available. This should prevent slowdowns
and potential stalls when memory is low and/or fragmented.

Signed-Off-By: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Dave Chinner 2018-03-06 17:03:28 -08:00 • committed by Darrick J. Wong
parent 0c8efd610b
commit cb0a8d2302
3 changed files with 11 additions and 5 deletions
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6
fs/xfs/kmem.c
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@ -46,13 +46,13 @@ kmem_alloc(size_t size, xfs_km_flags_t flags)
}
void *
kmem_zalloc_large(size_t size, xfs_km_flags_t flags)
kmem_alloc_large(size_t size, xfs_km_flags_t flags)
{
unsigned nofs_flag = 0;
void *ptr;
gfp_t lflags;
ptr = kmem_zalloc(size, flags | KM_MAYFAIL);
ptr = kmem_alloc(size, flags | KM_MAYFAIL);
if (ptr)
return ptr;
@ -67,7 +67,7 @@ kmem_zalloc_large(size_t size, xfs_km_flags_t flags)
nofs_flag = memalloc_nofs_save();
lflags = kmem_flags_convert(flags);
ptr = __vmalloc(size, lflags | __GFP_ZERO, PAGE_KERNEL);
ptr = __vmalloc(size, lflags, PAGE_KERNEL);
if (flags & KM_NOFS)
memalloc_nofs_restore(nofs_flag);