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swap_pager_meta_free() frees allocated blocks in a way that

Browse source 
exploits the sparsity of allocated blocks in a range, without
issuing an "are you there?" query for every block in the range.
swap_pager_copy() is not so smart.  Modify the implementation
of swap_pager_meta_free() slightly so that swap_pager_copy()
can use that smarter implementation too.

Based on an observation of: Yoshihiro Ota (ota_j.email.ne.jp)
Reviewed by: kib,alc
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D22280
This commit is contained in:
Doug Moore 2019-11-11 16:59:49 +00:00
parent c17cd08f53
commit 467057fcd9
1 changed files with 84 additions and 68 deletions
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152
sys/vm/swap_pager.c
View file

@ -422,6 +422,8 @@ static daddr_t swp_pager_getswapspace(int *npages, int limit);
*/
static daddr_t swp_pager_meta_build(vm_object_t, vm_pindex_t, daddr_t);
static void swp_pager_meta_free(vm_object_t, vm_pindex_t, vm_pindex_t);
static void swp_pager_meta_transfer(vm_object_t src, vm_object_t dst,
vm_pindex_t pindex, vm_pindex_t count);
static void swp_pager_meta_free_all(vm_object_t);
static daddr_t swp_pager_meta_ctl(vm_object_t, vm_pindex_t, int);
@ -933,6 +935,33 @@ swap_pager_reserve(vm_object_t object, vm_pindex_t start, vm_size_t size)
return (0);
}
static bool
swp_pager_xfer_source(vm_object_t srcobject, vm_object_t dstobject,
vm_pindex_t pindex, daddr_t addr)
{
daddr_t dstaddr;
if (swp_pager_meta_ctl(dstobject, pindex, 0) != SWAPBLK_NONE) {
/* Caller should destroy the source block. */
return (false);
}
/*
* Destination has no swapblk and is not resident, transfer source.
* swp_pager_meta_build() can sleep.
*/
vm_object_pip_add(srcobject, 1);
VM_OBJECT_WUNLOCK(srcobject);
vm_object_pip_add(dstobject, 1);
dstaddr = swp_pager_meta_build(dstobject, pindex, addr);
KASSERT(dstaddr == SWAPBLK_NONE,
("Unexpected destination swapblk"));
vm_object_pip_wakeup(dstobject);
VM_OBJECT_WLOCK(srcobject);
vm_object_pip_wakeup(srcobject);
return (true);
}
/*
* SWAP_PAGER_COPY() - copy blocks from source pager to destination pager
* and destroy the source.
@ -956,8 +985,6 @@ void
swap_pager_copy(vm_object_t srcobject, vm_object_t dstobject,
vm_pindex_t offset, int destroysource)
{
vm_pindex_t i;
daddr_t dstaddr, n_free, s_free, srcaddr;
VM_OBJECT_ASSERT_WLOCKED(srcobject);
VM_OBJECT_ASSERT_WLOCKED(dstobject);
@ -984,38 +1011,7 @@ swap_pager_copy(vm_object_t srcobject, vm_object_t dstobject,
/*
* Transfer source to destination.
*/
swp_pager_init_freerange(&s_free, &n_free);
for (i = 0; i < dstobject->size; ++i) {
srcaddr = swp_pager_meta_ctl(srcobject, i + offset, SWM_POP);
if (srcaddr == SWAPBLK_NONE)
continue;
dstaddr = swp_pager_meta_ctl(dstobject, i, 0);
if (dstaddr != SWAPBLK_NONE) {
/*
* Destination has valid swapblk or it is represented
* by a resident page. We destroy the source block.
*/
swp_pager_update_freerange(&s_free, &n_free, srcaddr);
continue;
}
/*
* Destination has no swapblk and is not resident,
* copy source.
*
* swp_pager_meta_build() can sleep.
*/
vm_object_pip_add(srcobject, 1);
VM_OBJECT_WUNLOCK(srcobject);
vm_object_pip_add(dstobject, 1);
dstaddr = swp_pager_meta_build(dstobject, i, srcaddr);
KASSERT(dstaddr == SWAPBLK_NONE,
("Unexpected destination swapblk"));
vm_object_pip_wakeup(dstobject);
VM_OBJECT_WLOCK(srcobject);
vm_object_pip_wakeup(srcobject);
}
swp_pager_freeswapspace(s_free, n_free);
swp_pager_meta_transfer(srcobject, dstobject, offset, dstobject->size);
/*
* Free left over swap blocks in source.
@ -2002,6 +1998,59 @@ allocated:
return (prev_swapblk);
}
/*
* SWP_PAGER_META_TRANSFER() - free a range of blocks in the srcobject's swap
* metadata, or transfer it into dstobject.
*
* This routine will free swap metadata structures as they are cleaned
* out.
*/
static void
swp_pager_meta_transfer(vm_object_t srcobject, vm_object_t dstobject,
vm_pindex_t pindex, vm_pindex_t count)
{
struct swblk *sb;
daddr_t n_free, s_free;
vm_pindex_t offset, last;
int i, limit, start;
VM_OBJECT_ASSERT_WLOCKED(srcobject);
if (srcobject->type != OBJT_SWAP || count == 0)
return;
swp_pager_init_freerange(&s_free, &n_free);
offset = pindex;
last = pindex + count;
for (;;) {
sb = SWAP_PCTRIE_LOOKUP_GE(&srcobject->un_pager.swp.swp_blks,
rounddown(pindex, SWAP_META_PAGES));
if (sb == NULL || sb->p >= last)
break;
start = pindex > sb->p ? pindex - sb->p : 0;
limit = last - sb->p < SWAP_META_PAGES ? last - sb->p :
SWAP_META_PAGES;
for (i = start; i < limit; i++) {
if (sb->d[i] == SWAPBLK_NONE)
continue;
if (dstobject == NULL ||
!swp_pager_xfer_source(srcobject, dstobject,
sb->p + i - offset, sb->d[i])) {
swp_pager_update_freerange(&s_free, &n_free,
sb->d[i]);
}
sb->d[i] = SWAPBLK_NONE;
}
pindex = sb->p + SWAP_META_PAGES;
if (swp_pager_swblk_empty(sb, 0, start) &&
swp_pager_swblk_empty(sb, limit, SWAP_META_PAGES)) {
SWAP_PCTRIE_REMOVE(&srcobject->un_pager.swp.swp_blks,
sb->p);
uma_zfree(swblk_zone, sb);
}
}
swp_pager_freeswapspace(s_free, n_free);
}
/*
* SWP_PAGER_META_FREE() - free a range of blocks in the object's swap metadata
*
@ -2015,40 +2064,7 @@ allocated:
static void
swp_pager_meta_free(vm_object_t object, vm_pindex_t pindex, vm_pindex_t count)
{
struct swblk *sb;
daddr_t n_free, s_free;
vm_pindex_t last;
int i, limit, start;
VM_OBJECT_ASSERT_WLOCKED(object);
if (object->type != OBJT_SWAP || count == 0)
return;
swp_pager_init_freerange(&s_free, &n_free);
last = pindex + count;
for (;;) {
sb = SWAP_PCTRIE_LOOKUP_GE(&object->un_pager.swp.swp_blks,
rounddown(pindex, SWAP_META_PAGES));
if (sb == NULL || sb->p >= last)
break;
start = pindex > sb->p ? pindex - sb->p : 0;
limit = last - sb->p < SWAP_META_PAGES ? last - sb->p :
SWAP_META_PAGES;
for (i = start; i < limit; i++) {
if (sb->d[i] == SWAPBLK_NONE)
continue;
swp_pager_update_freerange(&s_free, &n_free, sb->d[i]);
sb->d[i] = SWAPBLK_NONE;
}
pindex = sb->p + SWAP_META_PAGES;
if (swp_pager_swblk_empty(sb, 0, start) &&
swp_pager_swblk_empty(sb, limit, SWAP_META_PAGES)) {
SWAP_PCTRIE_REMOVE(&object->un_pager.swp.swp_blks,
sb->p);
uma_zfree(swblk_zone, sb);
}
}
swp_pager_freeswapspace(s_free, n_free);
swp_pager_meta_transfer(object, NULL, pindex, count);
}
/*