The patch titled
Subject: mm: add support for __GFP_ZERO flag to dma_pool_alloc()
has been added to the -mm tree. Its filename is
mm-add-support-for-__gfp_zero-flag-to-dma_pool_alloc.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-add-support-for-__gfp_zero-flag-to-dma_pool_alloc.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-add-support-for-__gfp_zero-flag-to-dma_pool_alloc.patch
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------------------------------------------------------
From: "Sean O. Stalley" <sean.stalley@xxxxxxxxx>
Subject: 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()
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@xxxxxxxxx>
Cc: Vinod Koul <vinod.koul@xxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: Gilles Muller <Gilles.Muller@xxxxxxx>
Cc: Nicolas Palix <nicolas.palix@xxxxxxx>
Cc: Michal Marek <mmarek@xxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/dmapool.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff -puN mm/dmapool.c~mm-add-support-for-__gfp_zero-flag-to-dma_pool_alloc mm/dmapool.c
--- a/mm/dmapool.c~mm-add-support-for-__gfp_zero-flag-to-dma_pool_alloc
+++ a/mm/dmapool.c
@@ -337,7 +337,7 @@ void *dma_pool_alloc(struct dma_pool *po
/* 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 *po
break;
}
}
- memset(retval, POOL_POISON_ALLOCATED, pool->size);
+ if (!(mem_flags & __GFP_ZERO))
+ memset(retval, POOL_POISON_ALLOCATED, pool->size);
#endif
spin_unlock_irqrestore(&pool->lock, flags);
+
+ if (mem_flags & __GFP_ZERO)
+ memset(retval, 0, pool->size);
+
return retval;
}
EXPORT_SYMBOL(dma_pool_alloc);
_
Patches currently in -mm which might be from sean.stalley@xxxxxxxxx are
mm-add-support-for-__gfp_zero-flag-to-dma_pool_alloc.patch
mm-add-dma_pool_zalloc-call-to-dma-api.patch
pci-mm-add-pci_pool_zalloc-call.patch
coccinelle-mm-scripts-coccinelle-api-alloc-pool_zalloc-simplecocci.patch
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