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Fix the background laundering mechanism after r329882.

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Rather than using the number of inactive queue scans as a metric for
how many clean pages are being freed by the page daemon, have the
page daemon keep a running counter of the number of pages it has freed,
and have the laundry thread use that when computing the background
laundering threshold.

Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D14884
This commit is contained in:
Mark Johnston 2018-03-29 14:27:40 +00:00
parent 222ab3169e
commit 6068486258
2 changed files with 19 additions and 20 deletions
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32
sys/vm/vm_pageout.c
View File

@ -943,8 +943,7 @@ vm_pageout_laundry_worker(void *arg)
{
struct vm_domain *vmd;
struct vm_pagequeue *pq;
uint64_t nclean, ndirty;
u_int inactq_scans, last_launder;
uint64_t nclean, ndirty, nfreed;
int domain, last_target, launder, shortfall, shortfall_cycle, target;
bool in_shortfall;
@ -958,8 +957,7 @@ vm_pageout_laundry_worker(void *arg)
in_shortfall = false;
shortfall_cycle = 0;
target = 0;
inactq_scans = 0;
last_launder = 0;
nfreed = 0;
/*
* Calls to these handlers are serialized by the swap syscall lock.
@ -1000,7 +998,6 @@ vm_pageout_laundry_worker(void *arg)
target = 0;
goto trybackground;
}
last_launder = inactq_scans;
launder = target / shortfall_cycle--;
goto dolaundry;
@ -1009,24 +1006,23 @@ vm_pageout_laundry_worker(void *arg)
* meet the conditions to perform background laundering:
*
* 1. The ratio of dirty to clean inactive pages exceeds the
* background laundering threshold and the pagedaemon has
* been woken up to reclaim pages since our last
* laundering, or
* background laundering threshold, or
* 2. we haven't yet reached the target of the current
* background laundering run.
*
* The background laundering threshold is not a constant.
* Instead, it is a slowly growing function of the number of
* page daemon scans since the last laundering. Thus, as the
* ratio of dirty to clean inactive pages grows, the amount of
* memory pressure required to trigger laundering decreases.
* clean pages freed by the page daemon since the last
* background laundering. Thus, as the ratio of dirty to
* clean inactive pages grows, the amount of memory pressure
* required to trigger laundering decreases.
*/
trybackground:
nclean = vmd->vmd_free_count +
vmd->vmd_pagequeues[PQ_INACTIVE].pq_cnt;
ndirty = vmd->vmd_pagequeues[PQ_LAUNDRY].pq_cnt;
if (target == 0 && inactq_scans != last_launder &&
ndirty * isqrt(inactq_scans - last_launder) >= nclean) {
if (target == 0 && ndirty * isqrt(nfreed /
(vmd->vmd_free_target - vmd->vmd_free_min)) >= nclean) {
target = vmd->vmd_background_launder_target;
}
@ -1039,8 +1035,8 @@ trybackground:
* proceed at the background laundering rate.
*/
if (target > 0) {
if (inactq_scans != last_launder) {
last_launder = inactq_scans;
if (nfreed > 0) {
nfreed = 0;
last_target = target;
} else if (last_target - target >=
vm_background_launder_max * PAGE_SIZE / 1024) {
@ -1089,7 +1085,8 @@ dolaundry:
if (target == 0)
vmd->vmd_laundry_request = VM_LAUNDRY_IDLE;
inactq_scans = vmd->vmd_inactq_scans;
nfreed += vmd->vmd_clean_pages_freed;
vmd->vmd_clean_pages_freed = 0;
vm_pagequeue_unlock(pq);
}
}
@ -1367,7 +1364,8 @@ drop_page:
VM_LAUNDRY_BACKGROUND;
wakeup(&vmd->vmd_laundry_request);
}
vmd->vmd_inactq_scans++;
vmd->vmd_clean_pages_freed +=
starting_page_shortage - page_shortage;
vm_pagequeue_unlock(pq);
}

7
sys/vm/vm_pagequeue.h
View File

@ -86,6 +86,7 @@ struct sysctl_oid;
* d vm_domainset_lock
* a atomic
* c const after boot
* q page queue lock
*/
struct vm_domain {
struct vm_pagequeue vmd_pagequeues[PQ_COUNT];
@ -112,15 +113,15 @@ struct vm_domain {
int vmd_pageout_pages_needed; /* (d) page daemon waiting for pages? */
bool vmd_minset; /* (d) Are we in vm_min_domains? */
bool vmd_severeset; /* (d) Are we in vm_severe_domains? */
int vmd_inactq_scans;
enum {
VM_LAUNDRY_IDLE = 0,
VM_LAUNDRY_BACKGROUND,
VM_LAUNDRY_SHORTFALL
} vmd_laundry_request;
/* Paging thresholds. */
u_int vmd_background_launder_target;
/* Paging thresholds and targets. */
u_int vmd_clean_pages_freed; /* (q) accumulator for laundry thread */
u_int vmd_background_launder_target; /* (c) */
u_int vmd_free_reserved; /* (c) pages reserved for deadlock */
u_int vmd_free_target; /* (c) pages desired free */
u_int vmd_free_min; /* (c) pages desired free */