diff options
Diffstat (limited to 'mm/page_counter.c')
| -rw-r--r-- | mm/page_counter.c | 29 |
1 files changed, 21 insertions, 8 deletions
diff --git a/mm/page_counter.c b/mm/page_counter.c index 3887bd152b75..b249d15af9dd 100644 --- a/mm/page_counter.c +++ b/mm/page_counter.c @@ -87,9 +87,22 @@ void page_counter_charge(struct page_counter *counter, unsigned long nr_pages) /* * This is indeed racy, but we can live with some * inaccuracy in the watermark. + * + * Notably, we have two watermarks to allow for both a globally + * visible peak and one that can be reset at a smaller scope. + * + * Since we reset both watermarks when the global reset occurs, + * we can guarantee that watermark >= local_watermark, so we + * don't need to do both comparisons every time. + * + * On systems with branch predictors, the inner condition should + * be almost free. */ - if (new > READ_ONCE(c->watermark)) - WRITE_ONCE(c->watermark, new); + if (new > READ_ONCE(c->local_watermark)) { + WRITE_ONCE(c->local_watermark, new); + if (new > READ_ONCE(c->watermark)) + WRITE_ONCE(c->watermark, new); + } } } @@ -140,12 +153,12 @@ bool page_counter_try_charge(struct page_counter *counter, if (protection) propagate_protected_usage(c, new); - /* - * Just like with failcnt, we can live with some - * inaccuracy in the watermark. - */ - if (new > READ_ONCE(c->watermark)) - WRITE_ONCE(c->watermark, new); + /* see comment on page_counter_charge */ + if (new > READ_ONCE(c->local_watermark)) { + WRITE_ONCE(c->local_watermark, new); + if (new > READ_ONCE(c->watermark)) + WRITE_ONCE(c->watermark, new); + } } return true; |