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Revision 251b97f552b1ad414cc5a9ccc8e4e94503edd5fc authored by Peter Zijlstra on 04 July 2008, 16:59:24 UTC, committed by Linus Torvalds on 04 July 2008, 17:40:04 UTC 
mm: dirty page accounting vs VM_MIXEDMAP
 
Dirty page accounting accurately measures the amound of dirty pages in
writable shared mappings by mapping the pages RO (as indicated by
vma_wants_writenotify).  We then trap on first write and call
set_page_dirty() on the page, after which we map the page RW and
continue execution.

When we launder dirty pages, we call clear_page_dirty_for_io() which
clears both the dirty flag, and maps the page RO again before we start
writeout so that the story can repeat itself.

vma_wants_writenotify() excludes VM_PFNMAP on the basis that we cannot
do the regular dirty page stuff on raw PFNs and the memory isn't going
anywhere anyway.

The recently introduced VM_MIXEDMAP mixes both !pfn_valid() and
pfn_valid() pages in a single mapping.

We can't do dirty page accounting on !pfn_valid() pages as stated
above, and mapping them RO causes them to be COW'ed on write, which
breaks VM_SHARED semantics.

Excluding VM_MIXEDMAP in vma_wants_writenotify() would mean we don't do
the regular dirty page accounting for the pfn_valid() pages, which
would bring back all the head-aches from inaccurate dirty page
accounting.

So instead, we let the !pfn_valid() pages get mapped RO, but fix them
up unconditionally in the fault path.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Acked-by: Hugh Dickins <hugh@veritas.com>
Cc: "Jared Hulbert" <jaredeh@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent cde5353
Raw File
prio_heap.c 
/*
 * Simple insertion-only static-sized priority heap containing
 * pointers, based on CLR, chapter 7
 */

#include <linux/slab.h>
#include <linux/prio_heap.h>

int heap_init(struct ptr_heap *heap, size_t size, gfp_t gfp_mask,
	      int (*gt)(void *, void *))
{
	heap->ptrs = kmalloc(size, gfp_mask);
	if (!heap->ptrs)
		return -ENOMEM;
	heap->size = 0;
	heap->max = size / sizeof(void *);
	heap->gt = gt;
	return 0;
}

void heap_free(struct ptr_heap *heap)
{
	kfree(heap->ptrs);
}

void *heap_insert(struct ptr_heap *heap, void *p)
{
	void *res;
	void **ptrs = heap->ptrs;
	int pos;

	if (heap->size < heap->max) {
		/* Heap insertion */
		int pos = heap->size++;
		while (pos > 0 && heap->gt(p, ptrs[(pos-1)/2])) {
			ptrs[pos] = ptrs[(pos-1)/2];
			pos = (pos-1)/2;
		}
		ptrs[pos] = p;
		return NULL;
	}

	/* The heap is full, so something will have to be dropped */

	/* If the new pointer is greater than the current max, drop it */
	if (heap->gt(p, ptrs[0]))
		return p;

	/* Replace the current max and heapify */
	res = ptrs[0];
	ptrs[0] = p;
	pos = 0;

	while (1) {
		int left = 2 * pos + 1;
		int right = 2 * pos + 2;
		int largest = pos;
		if (left < heap->size && heap->gt(ptrs[left], p))
			largest = left;
		if (right < heap->size && heap->gt(ptrs[right], ptrs[largest]))
			largest = right;
		if (largest == pos)
			break;
		/* Push p down the heap one level and bump one up */
		ptrs[pos] = ptrs[largest];
		ptrs[largest] = p;
		pos = largest;
	}
	return res;
}
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