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bitmap: add atomic test and clear

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The new bitmap_test_and_clear_atomic() function clears a range and
returns whether or not the bits were set.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <1417519399-3166-3-git-send-email-stefanha@redhat.com>
[Test before xchg; then a full barrier is needed at the end just like
 in the previous patch.  The barrier can be avoided if we did at least
 one xchg.  - Paolo]
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2014-12-02 11:23:15 +00:00 • committed by Paolo Bonzini
parent 9f02cfc84b
commit 36546e5b80
2 changed files with 47 additions and 0 deletions
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45
util/bitmap.c
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@ -235,6 +235,51 @@ void bitmap_clear(unsigned long *map, long start, long nr)
}
}
bool bitmap_test_and_clear_atomic(unsigned long *map, long start, long nr)
{
unsigned long *p = map + BIT_WORD(start);
const long size = start + nr;
int bits_to_clear = BITS_PER_LONG - (start % BITS_PER_LONG);
unsigned long mask_to_clear = BITMAP_FIRST_WORD_MASK(start);
unsigned long dirty = 0;
unsigned long old_bits;
/* First word */
if (nr - bits_to_clear > 0) {
old_bits = atomic_fetch_and(p, ~mask_to_clear);
dirty |= old_bits & mask_to_clear;
nr -= bits_to_clear;
bits_to_clear = BITS_PER_LONG;
mask_to_clear = ~0UL;
p++;
}
/* Full words */
if (bits_to_clear == BITS_PER_LONG) {
while (nr >= BITS_PER_LONG) {
if (*p) {
old_bits = atomic_xchg(p, 0);
dirty |= old_bits;
}
nr -= BITS_PER_LONG;
p++;
}
}
/* Last word */
if (nr) {
mask_to_clear &= BITMAP_LAST_WORD_MASK(size);
old_bits = atomic_fetch_and(p, ~mask_to_clear);
dirty |= old_bits & mask_to_clear;
} else {
if (!dirty) {
smp_mb();
}
}
return dirty != 0;
}
#define ALIGN_MASK(x,mask) (((x)+(mask))&~(mask))
/**