Revision d7831a0bdf06b9f722b947bb0c205ff7d77cebd8 authored by Richard Kennedy on 30 June 2009, 18:41:35 UTC, committed by Linus Torvalds on 01 July 2009, 01:56:01 UTC
balance_dirty_pages can overreact and move all of the dirty pages to writeback unnecessarily. balance_dirty_pages makes its decision to throttle based on the number of dirty plus writeback pages that are over the calculated limit,so it will continue to move pages even when there are plenty of pages in writeback and less than the threshold still dirty. This allows it to overshoot its limits and move all the dirty pages to writeback while waiting for the drives to catch up and empty the writeback list. A simple fio test easily demonstrates this problem. fio --name=f1 --directory=/disk1 --size=2G -rw=write --name=f2 --directory=/disk2 --size=1G --rw=write --startdelay=10 This is the simplest fix I could find, but I'm not entirely sure that it alone will be enough for all cases. But it certainly is an improvement on my desktop machine writing to 2 disks. Do we need something more for machines with large arrays where bdi_threshold * number_of_drives is greater than the dirty_ratio ? Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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iommu-helpers.h
/**
* iommu_fill_pdir - Insert coalesced scatter/gather chunks into the I/O Pdir.
* @ioc: The I/O Controller.
* @startsg: The scatter/gather list of coalesced chunks.
* @nents: The number of entries in the scatter/gather list.
* @hint: The DMA Hint.
*
* This function inserts the coalesced scatter/gather list chunks into the
* I/O Controller's I/O Pdir.
*/
static inline unsigned int
iommu_fill_pdir(struct ioc *ioc, struct scatterlist *startsg, int nents,
unsigned long hint,
void (*iommu_io_pdir_entry)(u64 *, space_t, unsigned long,
unsigned long))
{
struct scatterlist *dma_sg = startsg; /* pointer to current DMA */
unsigned int n_mappings = 0;
unsigned long dma_offset = 0, dma_len = 0;
u64 *pdirp = NULL;
/* Horrible hack. For efficiency's sake, dma_sg starts one
* entry below the true start (it is immediately incremented
* in the loop) */
dma_sg--;
while (nents-- > 0) {
unsigned long vaddr;
long size;
DBG_RUN_SG(" %d : %08lx/%05x %08lx/%05x\n", nents,
(unsigned long)sg_dma_address(startsg), cnt,
sg_virt_addr(startsg), startsg->length
);
/*
** Look for the start of a new DMA stream
*/
if (sg_dma_address(startsg) & PIDE_FLAG) {
u32 pide = sg_dma_address(startsg) & ~PIDE_FLAG;
BUG_ON(pdirp && (dma_len != sg_dma_len(dma_sg)));
dma_sg++;
dma_len = sg_dma_len(startsg);
sg_dma_len(startsg) = 0;
dma_offset = (unsigned long) pide & ~IOVP_MASK;
n_mappings++;
#if defined(ZX1_SUPPORT)
/* Pluto IOMMU IO Virt Address is not zero based */
sg_dma_address(dma_sg) = pide | ioc->ibase;
#else
/* SBA, ccio, and dino are zero based.
* Trying to save a few CPU cycles for most users.
*/
sg_dma_address(dma_sg) = pide;
#endif
pdirp = &(ioc->pdir_base[pide >> IOVP_SHIFT]);
prefetchw(pdirp);
}
BUG_ON(pdirp == NULL);
vaddr = sg_virt_addr(startsg);
sg_dma_len(dma_sg) += startsg->length;
size = startsg->length + dma_offset;
dma_offset = 0;
#ifdef IOMMU_MAP_STATS
ioc->msg_pages += startsg->length >> IOVP_SHIFT;
#endif
do {
iommu_io_pdir_entry(pdirp, KERNEL_SPACE,
vaddr, hint);
vaddr += IOVP_SIZE;
size -= IOVP_SIZE;
pdirp++;
} while(unlikely(size > 0));
startsg++;
}
return(n_mappings);
}
/*
** First pass is to walk the SG list and determine where the breaks are
** in the DMA stream. Allocates PDIR entries but does not fill them.
** Returns the number of DMA chunks.
**
** Doing the fill separate from the coalescing/allocation keeps the
** code simpler. Future enhancement could make one pass through
** the sglist do both.
*/
static inline unsigned int
iommu_coalesce_chunks(struct ioc *ioc, struct device *dev,
struct scatterlist *startsg, int nents,
int (*iommu_alloc_range)(struct ioc *, struct device *, size_t))
{
struct scatterlist *contig_sg; /* contig chunk head */
unsigned long dma_offset, dma_len; /* start/len of DMA stream */
unsigned int n_mappings = 0;
unsigned int max_seg_size = dma_get_max_seg_size(dev);
while (nents > 0) {
/*
** Prepare for first/next DMA stream
*/
contig_sg = startsg;
dma_len = startsg->length;
dma_offset = sg_virt_addr(startsg) & ~IOVP_MASK;
/* PARANOID: clear entries */
sg_dma_address(startsg) = 0;
sg_dma_len(startsg) = 0;
/*
** This loop terminates one iteration "early" since
** it's always looking one "ahead".
*/
while(--nents > 0) {
unsigned long prevstartsg_end, startsg_end;
prevstartsg_end = sg_virt_addr(startsg) +
startsg->length;
startsg++;
startsg_end = sg_virt_addr(startsg) +
startsg->length;
/* PARANOID: clear entries */
sg_dma_address(startsg) = 0;
sg_dma_len(startsg) = 0;
/*
** First make sure current dma stream won't
** exceed DMA_CHUNK_SIZE if we coalesce the
** next entry.
*/
if(unlikely(ALIGN(dma_len + dma_offset + startsg->length,
IOVP_SIZE) > DMA_CHUNK_SIZE))
break;
if (startsg->length + dma_len > max_seg_size)
break;
/*
** Next see if we can append the next chunk (i.e.
** it must end on one page and begin on another
*/
if (unlikely(((prevstartsg_end | sg_virt_addr(startsg)) & ~PAGE_MASK) != 0))
break;
dma_len += startsg->length;
}
/*
** End of DMA Stream
** Terminate last VCONTIG block.
** Allocate space for DMA stream.
*/
sg_dma_len(contig_sg) = dma_len;
dma_len = ALIGN(dma_len + dma_offset, IOVP_SIZE);
sg_dma_address(contig_sg) =
PIDE_FLAG
| (iommu_alloc_range(ioc, dev, dma_len) << IOVP_SHIFT)
| dma_offset;
n_mappings++;
}
return n_mappings;
}
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