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Callers of swp_pager_getswapspace get either as many blocks as they

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requested, or none, and in the latter case it is up to them to pick a
smaller request to make - which they always do by halving the failed
request. This change to swp_pager_getswapspace leaves the task of
downsizing the request to the function and not its caller. It still
does so by halving the original request.

Approved by: kib (mentor)
Differential Revision: https://reviews.freebsd.org/D20228
This commit is contained in:
Doug Moore 2019-05-11 10:16:43 +00:00
parent 535192530c
commit 48e98a2afc
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=347487
1 changed files with 50 additions and 58 deletions
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108
sys/vm/swap_pager.c
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@ -407,7 +407,7 @@ static int swapoff_one(struct swdevt *sp, struct ucred *cred);
* Swap bitmap functions
*/
static void swp_pager_freeswapspace(daddr_t blk, daddr_t npages);
static daddr_t swp_pager_getswapspace(int npages);
static daddr_t swp_pager_getswapspace(int *npages, int limit);
/*
* Metadata functions
@ -708,9 +708,10 @@ swap_pager_dealloc(vm_object_t object)
/*
* SWP_PAGER_GETSWAPSPACE() - allocate raw swap space
*
* Allocate swap for the requested number of pages. The starting
* swap block number (a page index) is returned or SWAPBLK_NONE
* if the allocation failed.
* Allocate swap for up to the requested number of pages, and at
* least a minimum number of pages. The starting swap block number
* (a page index) is returned or SWAPBLK_NONE if the allocation
* failed.
*
* Also has the side effect of advising that somebody made a mistake
* when they configured swap and didn't configure enough.
@ -720,38 +721,46 @@ swap_pager_dealloc(vm_object_t object)
* We allocate in round-robin fashion from the configured devices.
*/
static daddr_t
swp_pager_getswapspace(int npages)
swp_pager_getswapspace(int *io_npages, int limit)
{
daddr_t blk;
struct swdevt *sp;
int i;
int npages;
blk = SWAPBLK_NONE;
npages = *io_npages;
mtx_lock(&sw_dev_mtx);
sp = swdevhd;
for (i = 0; i < nswapdev; i++) {
while (!TAILQ_EMPTY(&swtailq)) {
if (sp == NULL)
sp = TAILQ_FIRST(&swtailq);
if (!(sp->sw_flags & SW_CLOSING)) {
if ((sp->sw_flags & SW_CLOSING) == 0)
blk = blist_alloc(sp->sw_blist, npages);
if (blk != SWAPBLK_NONE) {
blk += sp->sw_first;
sp->sw_used += npages;
swap_pager_avail -= npages;
swp_sizecheck();
swdevhd = TAILQ_NEXT(sp, sw_list);
goto done;
}
}
if (blk != SWAPBLK_NONE)
break;
sp = TAILQ_NEXT(sp, sw_list);
if (swdevhd == sp) {
if (npages <= limit)
break;
npages >>= 1;
}
}
if (swap_pager_full != 2) {
printf("swap_pager_getswapspace(%d): failed\n", npages);
swap_pager_full = 2;
swap_pager_almost_full = 1;
if (blk != SWAPBLK_NONE) {
*io_npages = npages;
blk += sp->sw_first;
sp->sw_used += npages;
swap_pager_avail -= npages;
swp_sizecheck();
swdevhd = TAILQ_NEXT(sp, sw_list);
} else {
if (swap_pager_full != 2) {
printf("swp_pager_getswapspace(%d): failed\n",
*io_npages);
swap_pager_full = 2;
swap_pager_almost_full = 1;
}
swdevhd = NULL;
}
swdevhd = NULL;
done:
mtx_unlock(&sw_dev_mtx);
return (blk);
}
@ -886,35 +895,28 @@ swap_pager_freespace(vm_object_t object, vm_pindex_t start, vm_size_t size)
int
swap_pager_reserve(vm_object_t object, vm_pindex_t start, vm_size_t size)
{
int n = 0;
daddr_t blk = SWAPBLK_NONE;
vm_pindex_t beg = start; /* save start index */
daddr_t addr, n_free, s_free;
daddr_t addr, blk, n_free, s_free;
int i, j, n;
swp_pager_init_freerange(&s_free, &n_free);
VM_OBJECT_WLOCK(object);
while (size) {
if (n == 0) {
n = BLIST_MAX_ALLOC;
while ((blk = swp_pager_getswapspace(n)) == SWAPBLK_NONE) {
n >>= 1;
if (n == 0) {
swp_pager_meta_free(object, beg, start - beg);
VM_OBJECT_WUNLOCK(object);
return (-1);
}
}
for (i = 0; i < size; i += n) {
n = min(BLIST_MAX_ALLOC, size - i);
blk = swp_pager_getswapspace(&n, 1);
if (blk == SWAPBLK_NONE) {
swp_pager_meta_free(object, start, i);
VM_OBJECT_WUNLOCK(object);
return (-1);
}
for (j = 0; j < n; ++j) {
addr = swp_pager_meta_build(object,
start + i + j, blk + j);
if (addr != SWAPBLK_NONE)
swp_pager_update_freerange(&s_free, &n_free,
addr);
}
addr = swp_pager_meta_build(object, start, blk);
if (addr != SWAPBLK_NONE)
swp_pager_update_freerange(&s_free, &n_free, addr);
--size;
++start;
++blk;
--n;
}
swp_pager_freeswapspace(s_free, n_free);
swp_pager_meta_free(object, start, n);
VM_OBJECT_WUNLOCK(object);
return (0);
}
@ -1384,18 +1386,8 @@ swap_pager_putpages(vm_object_t object, vm_page_t *ma, int count,
n = min(BLIST_MAX_ALLOC, count - i);
n = min(n, nsw_cluster_max);
/*
* Get biggest block of swap we can. If we fail, fall
* back and try to allocate a smaller block. Don't go
* overboard trying to allocate space if it would overly
* fragment swap.
*/
while (
(blk = swp_pager_getswapspace(n)) == SWAPBLK_NONE &&
n > 4
) {
n >>= 1;
}
/* Get a block of swap of size up to size n. */
blk = swp_pager_getswapspace(&n, 4);
if (blk == SWAPBLK_NONE) {
for (j = 0; j < n; ++j)
rtvals[i+j] = VM_PAGER_FAIL;