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vnode_pager: simplify loop, avoid overflow

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Filling in read-behind pages in vnode_pager_generic_getpages() is made
very slightly simpler here, by avoiding overflowing the startpindex
variable and then avoiding an extra test in the allocation loop that
handles the overflow case.

Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D49200
This commit is contained in:
Doug Moore 2025-03-02 02:13:24 -06:00
parent 23da585dd4
commit 420e2f8a74
1 changed files with 6 additions and 11 deletions
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17
sys/vm/vnode_pager.c
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@ -1045,18 +1045,13 @@ vnode_pager_generic_getpages(struct vnode *vp, vm_page_t *m, int count,
vm_page_t mpred, p;
VM_OBJECT_WLOCK(object);
startpindex = m[0]->pindex - rbehind;
if ((mpred = TAILQ_PREV(m[0], pglist, listq)) != NULL &&
mpred->pindex >= startpindex)
startpindex = mpred->pindex + 1;
tpindex = m[0]->pindex;
startpindex = MAX(tpindex, rbehind) - rbehind;
if ((mpred = TAILQ_PREV(m[0], pglist, listq)) != NULL)
startpindex = MAX(startpindex, mpred->pindex + 1);
/*
* tpindex is unsigned; beware of numeric underflow.
* Stepping backward from pindex, mpred doesn't change.
*/
for (tpindex = m[0]->pindex - 1;
tpindex >= startpindex && tpindex < m[0]->pindex;
tpindex--, i++) {
/* Stepping backward from pindex, mpred doesn't change. */
for (; tpindex-- > startpindex; i++) {
p = vm_page_alloc_after(object, tpindex,
VM_ALLOC_NORMAL, mpred);
if (p == NULL) {