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Commit cd0aca2d authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
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block: fix queue bounce limit setting 



Impact: don't set GFP_DMA in q->bounce_gfp unnecessarily

All DMA address limits are expressed in terms of the last addressable
unit (byte or page) instead of one plus that.  However, when
determining bounce_gfp for 64bit machines in blk_queue_bounce_limit(),
it compares the specified limit against 0x100000000UL to determine
whether it's below 4G ending up falsely setting GFP_DMA in
q->bounce_gfp.

As DMA zone is very small on x86_64, this makes larger SG_IO transfers
very eager to trigger OOM killer.  Fix it.  While at it, rename the
parameter to @dma_mask for clarity and convert comment to proper
winged style.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 25636e28

block/blk-settings.c

+11 −9
Original line number Diff line number Diff line
@@ -157,25 +157,27 @@ EXPORT_SYMBOL(blk_queue_make_request); 
/**

 * blk_queue_bounce_limit - set bounce buffer limit for queue

 * @q: the request queue for the device

 * @dma_addr:   bus address limit

 * @dma_mask: the maximum address the device can handle

 *

 * Description:

 *    Different hardware can have different requirements as to what pages

 *    it can do I/O directly to. A low level driver can call

 *    blk_queue_bounce_limit to have lower memory pages allocated as bounce

 *    buffers for doing I/O to pages residing above @dma_addr.

 *    buffers for doing I/O to pages residing above @dma_mask.

 **/

void blk_queue_bounce_limit(struct request_queue *q, u64 dma_addr)

void blk_queue_bounce_limit(struct request_queue *q, u64 dma_mask)

{

	unsigned long b_pfn = dma_addr >> PAGE_SHIFT;

	unsigned long b_pfn = dma_mask >> PAGE_SHIFT;

	int dma = 0;



	q->bounce_gfp = GFP_NOIO;

#if BITS_PER_LONG == 64

	/* Assume anything <= 4GB can be handled by IOMMU.

	   Actually some IOMMUs can handle everything, but I don't

	   know of a way to test this here. */

	if (b_pfn < (min_t(u64, 0x100000000UL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))

	/*

	 * Assume anything <= 4GB can be handled by IOMMU.  Actually

	 * some IOMMUs can handle everything, but I don't know of a

	 * way to test this here.

	 */

	if (b_pfn < (min_t(u64, 0xffffffffUL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))

		dma = 1;

	q->bounce_pfn = max_low_pfn;

#else