Commit 0e749e54 authored Jan 15, 2016 by Dan Williams Committed by Linus Torvalds Jan 15, 2016

dax: increase granularity of dax_clear_blocks() operations



dax_clear_blocks is currently performing a cond_resched() after every
PAGE_SIZE memset.  We need not check so frequently, for example md-raid
only calls cond_resched() at stripe granularity.  Also, in preparation
for introducing a dax_map_atomic() operation that temporarily pins a dax
mapping move the call to cond_resched() to the outer loop.

The worst case latency between calls to cond_resched() after this change
is 500us the average latency is 133us.  This is up from a 10us max and
4us average.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Jan Kara <jack@suse.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 52db400f

fs/dax.c

+8 −14

Original line number	Diff line number	Diff line
		@@ -28,6 +28,7 @@
		#include <linux/sched.h>
		#include <linux/uio.h>
		#include <linux/vmstat.h>
		#include <linux/sizes.h>

		/*
		* dax_clear_blocks() is called from within transaction context from XFS,
		@@ -43,24 +44,17 @@ int dax_clear_blocks(struct inode *inode, sector_t block, long size)
		do {
		void __pmem *addr;
		unsigned long pfn;
		long count;
		long count, sz;

		count = bdev_direct_access(bdev, sector, &addr, &pfn, size);
		if (count < 0)
		return count;
		BUG_ON(size < count);
		while (count > 0) {
		unsigned pgsz = PAGE_SIZE - offset_in_page(addr);
		if (pgsz > count)
		pgsz = count;
		clear_pmem(addr, pgsz);
		addr += pgsz;
		size -= pgsz;
		count -= pgsz;
		BUG_ON(pgsz & 511);
		sector += pgsz / 512;
		sz = min_t(long, count, SZ_128K);
		clear_pmem(addr, sz);
		size -= sz;
		BUG_ON(sz & 511);
		sector += sz / 512;
		cond_resched();
		}
		} while (size);

		wmb_pmem();

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