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mm: add support for __GFP_ZERO flag to dma_pool_alloc()

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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()
call.

There was some concern that this always calls memset() to zero, instead
of passing __GFP_ZERO into the page allocator.
[https://lkml.org/lkml/2015/7/15/881]

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: Sean O. Stalley <sean.stalley@intel.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Vinod Koul <vinod.koul@intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Gilles Muller <Gilles.Muller@lip6.fr>
Cc: Nicolas Palix <nicolas.palix@imag.fr>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Sean O. Stalley 2015-09-08 15:02:24 -07:00 committed by Linus Torvalds
parent c54839a722
commit fa23f56d90
1 changed files with 7 additions and 2 deletions
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9
mm/dmapool.c
View file

@ -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 */ /* pool_alloc_page() might sleep, so temporarily drop &pool->lock */
spin_unlock_irqrestore(&pool->lock, flags); spin_unlock_irqrestore(&pool->lock, flags);
page = pool_alloc_page(pool, mem_flags); page = pool_alloc_page(pool, mem_flags & (~__GFP_ZERO));
if (!page) if (!page)
return NULL; return NULL;
@ -375,9 +375,14 @@ void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
break; break;
} }
} }
memset(retval, POOL_POISON_ALLOCATED, pool->size); if (!(mem_flags & __GFP_ZERO))
memset(retval, POOL_POISON_ALLOCATED, pool->size);
#endif #endif
spin_unlock_irqrestore(&pool->lock, flags); spin_unlock_irqrestore(&pool->lock, flags);
if (mem_flags & __GFP_ZERO)
memset(retval, 0, pool->size);
return retval; return retval;
} }
EXPORT_SYMBOL(dma_pool_alloc); EXPORT_SYMBOL(dma_pool_alloc);