Commit fa23f56d authored by Sean O. Stalley's avatar Sean O. Stalley Committed by Linus Torvalds
Browse files

mm: add support for __GFP_ZERO flag to dma_pool_alloc()

Currently a call to dma_pool_alloc() with a ___GFP_ZERO flag returns a
non-zeroed memory region.

This patchset adds support for the __GFP_ZERO flag to dma_pool_alloc(),
adds 2 wrapper functions for allocing zeroed memory from a pool, and
provides a coccinelle script for finding & replacing instances of
dma_pool_alloc() followed by memset(0) with a single dma_pool_zalloc()

There was some concern that this always calls memset() to zero, instead
of passing __GFP_ZERO into the page allocator.


I ran a test on my system to get an idea of how often dma_pool_alloc()
calls into pool_alloc_page().

After Boot:	[   30.119863] alloc_calls:541, page_allocs:7
After an hour:	[ 3600.951031] alloc_calls:9566, page_allocs:12
After copying 1GB file onto a USB drive:
		[ 4260.657148] alloc_calls:17225, page_allocs:12

It doesn't look like dma_pool_alloc() calls down to the page allocator
very often (at least on my system).

This patch (of 4):

Currently the __GFP_ZERO flag is ignored by dma_pool_alloc().
Make dma_pool_alloc() zero the memory if this flag is set.

Signed-off-by: default avatarSean O. Stalley <>
Acked-by: default avatarDavid Rientjes <>
Cc: Vinod Koul <>
Cc: Bjorn Helgaas <>
Cc: Gilles Muller <>
Cc: Nicolas Palix <>
Cc: Michal Marek <>
Cc: Sebastian Andrzej Siewior <>
Cc: Jonathan Corbet <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent c54839a7
......@@ -337,7 +337,7 @@ void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
/* pool_alloc_page() might sleep, so temporarily drop &pool->lock */
spin_unlock_irqrestore(&pool->lock, flags);
page = pool_alloc_page(pool, mem_flags);
page = pool_alloc_page(pool, mem_flags & (~__GFP_ZERO));
if (!page)
return NULL;
......@@ -375,9 +375,14 @@ void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
memset(retval, POOL_POISON_ALLOCATED, pool->size);
if (!(mem_flags & __GFP_ZERO))
memset(retval, POOL_POISON_ALLOCATED, pool->size);
spin_unlock_irqrestore(&pool->lock, flags);
if (mem_flags & __GFP_ZERO)
memset(retval, 0, pool->size);
return retval;
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