On Wed, Aug 14, 2019 at 09:10:15PM -0500, Eric Blake wrote: > When sparse_array_zero() is used for a range larger than a page, > there's no need to waste time in memset() or is_zero() - we already > know the page will be free()d. > > Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; > --- > > Here's a fun one :) > > common/sparse/sparse.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/common/sparse/sparse.c b/common/sparse/sparse.c > index cb44743c..5e085763 100644 > --- a/common/sparse/sparse.c > +++ b/common/sparse/sparse.c > @@ -343,10 +343,13 @@ sparse_array_zero (struct sparse_array *sa, uint32_t count, uint64_t offset) > n = count; > > if (p) { > - memset (p, 0, n); > + if (n < PAGE_SIZE) > + memset (p, 0, n); > + else > + assert (p == *l2_page); > > /* If the whole page is now zero, free it. */ > - if (is_zero (*l2_page, PAGE_SIZE)) { > + if (n == PAGE_SIZE || is_zero (*l2_page, PAGE_SIZE)) { Should this be n >= PAGE_SIZE? My guess is no because lookup (..&n..) can't return n larger than the remaining size of the page (ie. n <= PAGE_SIZE).

> if (sa->debug) > nbdkit_debug ("%s: freeing zero page at offset %" PRIu64, > __func__, offset); Anyway, ACK. Rich.