__mod_zone_page_stat() is not irq-safe, so it should be used carefully. And it is not appropirately documented now. This patch adds comment for it, and also documents for some of its call sites.
Suggested-by: Andrew Morton <[email protected]> Signed-off-by: Jianyu Zhan <[email protected]> --- mm/page_alloc.c | 2 ++ mm/rmap.c | 6 ++++++ mm/vmstat.c | 16 +++++++++++++++- 3 files changed, 23 insertions(+), 1 deletion(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 5dba293..9d6f474 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -659,6 +659,8 @@ static inline int free_pages_check(struct page *page) * * And clear the zone's pages_scanned counter, to hold off the "all pages are * pinned" detection logic. + * + * Note: this function should be used with irq disabled. */ static void free_pcppages_bulk(struct zone *zone, int count, struct per_cpu_pages *pcp) diff --git a/mm/rmap.c b/mm/rmap.c index 9c3e773..6078a30 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -979,6 +979,8 @@ void page_add_anon_rmap(struct page *page, /* * Special version of the above for do_swap_page, which often runs * into pages that are exclusively owned by the current process. + * So we could use the irq-unsafe version __{inc|mod}_zone_page_stat + * here without others racing change it in between. * Everybody else should continue to use page_add_anon_rmap above. */ void do_page_add_anon_rmap(struct page *page, @@ -1077,6 +1079,10 @@ void page_remove_rmap(struct page *page) /* * Hugepages are not counted in NR_ANON_PAGES nor NR_FILE_MAPPED * and not charged by memcg for now. + * + * And we are the last user of this page, so it is safe to use + * the irq-unsafe version __{mod|dec}_zone_page here, since we + * have no racer. */ if (unlikely(PageHuge(page))) goto out; diff --git a/mm/vmstat.c b/mm/vmstat.c index 302dd07..778f154 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -207,7 +207,21 @@ void set_pgdat_percpu_threshold(pg_data_t *pgdat, } /* - * For use when we know that interrupts are disabled. + * Optimized modificatoin function. + * + * The code basically does the modification in two steps: + * + * 1. read the current counter based on the processor number + * 2. modificate the counter write it back. + * + * So this function should be used with the guarantee that + * + * 1. interrupts are disabled, or + * 2. interrupts are enabled, but no other sites would race to + * modify this counter in between. + * + * Otherwise, an irq-safe version mod_zone_page_state() should + * be used instead. */ void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item, int delta) -- 2.0.0-rc1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
