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Avoid unnecessary object locking in vm_page_grab_pages_unlocked().

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We were needlessly acquiring the object lock to call
vm_page_grab_pages() even when all of the requested pages were looked up
locklessly.  Fix that, stop testing for count == 0 in
vm_page_grab_pages(), and add assertions to help catch this kind of
mistake.

Reported by:	cem
Reviewed by:	alc, cem, dougm, jeff
Differential Revision:	https://reviews.freebsd.org/D26304
This commit is contained in:
Mark Johnston 2020-09-02 19:59:25 +00:00
parent ac07cdf8f7
commit a2d704d19f
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=365275
1 changed files with 5 additions and 4 deletions
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9
sys/vm/vm_page.c
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@ -4724,12 +4724,11 @@ vm_page_grab_pages(vm_object_t object, vm_pindex_t pindex, int allocflags,
VM_OBJECT_ASSERT_WLOCKED(object);
KASSERT(((u_int)allocflags >> VM_ALLOC_COUNT_SHIFT) == 0,
("vm_page_grap_pages: VM_ALLOC_COUNT() is not allowed"));
KASSERT(count > 0,
("vm_page_grab_pages: invalid page count %d", count));
vm_page_grab_check(allocflags);
pflags = vm_page_grab_pflags(allocflags);
if (count == 0)
return (0);
i = 0;
retrylookup:
m = vm_radix_lookup_le(&object->rtree, pindex + i);
@ -4783,6 +4782,8 @@ vm_page_grab_pages_unlocked(vm_object_t object, vm_pindex_t pindex,
int flags;
int i;
KASSERT(count > 0,
("vm_page_grab_pages_unlocked: invalid page count %d", count));
vm_page_grab_check(allocflags);
/*
@ -4805,7 +4806,7 @@ vm_page_grab_pages_unlocked(vm_object_t object, vm_pindex_t pindex,
vm_page_grab_release(m, allocflags);
pred = ma[i] = m;
}
if ((allocflags & VM_ALLOC_NOCREAT) != 0)
if (i == count || (allocflags & VM_ALLOC_NOCREAT) != 0)
return (i);
count -= i;
VM_OBJECT_WLOCK(object);