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psset: Purge empty slabs first.

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These are particularly good candidates for purging (listed in the diff).
This commit is contained in:
David Goldblatt
2021-06-03 16:21:29 -07:00
committed by David Goldblatt
parent 41fd56605e
commit 47d8a7e6b0
3 changed files with 143 additions and 7 deletions
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29
src/psset.c
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@@ -201,11 +201,32 @@ psset_purge_list_ind(hpdata_t *ps) {
size_t ndirty = hpdata_ndirty_get(ps);
/* Shouldn't have something with no dirty pages purgeable. */
assert(ndirty > 0);
/*
* Higher indices correspond to lists we'd like to purge earlier; make
* the two highest indices correspond to empty lists, which we attempt
* to purge before purging any non-empty list. This has two advantages:
* - Empty page slabs are the least likely to get reused (we'll only
* pick them for an allocation if we have no other choice).
* - Empty page slabs can purge every dirty page they contain in a
* single call, which is not usually the case.
*
* We purge hugeified empty slabs before nonhugeified ones, on the basis
* that they are fully dirty, while nonhugified slabs might not be, so
* we free up more pages more easily.
*/
if (hpdata_nactive_get(ps) == 0) {
if (hpdata_huge_get(ps)) {
return PSSET_NPURGE_LISTS - 1;
} else {
return PSSET_NPURGE_LISTS - 2;
}
}
pszind_t pind = sz_psz2ind(sz_psz_quantize_floor(ndirty << LG_PAGE));
/*
* Higher indices correspond to lists we'd like to purge earlier;
* increment the index for the nonhugified hpdatas first, so that we'll
* pick them before picking hugified ones.
* For non-empty slabs, we may reuse them again. Prefer purging
* non-hugeified slabs before hugeified ones then, among pages of
* similar dirtiness. We still get some benefit from the hugification.
*/
return (size_t)pind * 2 + (hpdata_huge_get(ps) ? 0 : 1);
}
@@ -321,7 +342,7 @@ psset_pick_purge(psset_t *psset) {
return NULL;
}
pszind_t ind = (pszind_t)ind_ssz;
assert(ind < PSSET_NPSIZES);
assert(ind < PSSET_NPURGE_LISTS);
hpdata_t *ps = hpdata_purge_list_first(&psset->to_purge[ind]);
assert(ps != NULL);
return ps;