On 08/27/2015 02:51 PM, Yaowei Bai wrote:
> The major portion of check_new_page() and free_pages_check() are same,
> introduce a helper function check_one_page() for simplification.
>
> Change in v3:
> - add the missed __PG_HWPOISON check per Michal Hocko
> Change in v2:
> - use bad_flags as parameter directly per Michal Hocko
>
> Signed-off-by: Yaowei Bai <bywxiaobai@xxxxxxx>
> ---
> mm/page_alloc.c | 54 +++++++++++++++++++++++-------------------------------
> 1 file changed, 23 insertions(+), 31 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5b5240b..0c9c82a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -707,10 +707,9 @@ out:
> zone->free_area[order].nr_free++;
> }
>
> -static inline int free_pages_check(struct page *page)
> +static inline int check_one_page(struct page *page, unsigned long bad_flags)
> {
> const char *bad_reason = NULL;
> - unsigned long bad_flags = 0;
>
> if (unlikely(page_mapcount(page)))
> bad_reason = "nonzero mapcount";
> @@ -718,9 +717,16 @@ static inline int free_pages_check(struct page *page)
> bad_reason = "non-NULL mapping";
> if (unlikely(atomic_read(&page->_count) != 0))
> bad_reason = "nonzero _count";
> - if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_FREE)) {
> - bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
> - bad_flags = PAGE_FLAGS_CHECK_AT_FREE;
> + if (bad_flags == PAGE_FLAGS_CHECK_AT_PREP) {
> + if (unlikely(page->flags & bad_flags))
> + bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
> + if (unlikely(page->flags & __PG_HWPOISON)) {
> + bad_reason = "HWPoisoned (hardware-corrupted)";
> + bad_flags = __PG_HWPOISON;
> + }
Before, HWPOISON was checked first, which means that it had lower priority than
PAGE_FLAGS_CHECK_AT_PREP (counter-intuitively). I can see why you switched that
though. You could fix that by changing the second nested "if" to "else if", but
I guess it doesn't matter. The "priorities" don't seem to be carefuly sorted anyway.
bloat-o-meter looks favorably with my gcc, although there shouldn't be a real
reason for it, as the inlining didn't change:
add/remove: 1/1 grow/shrink: 1/1 up/down: 285/-336 (-51)
function old new delta
bad_page - 276 +276
get_page_from_freelist 2521 2530 +9
free_pages_prepare 745 667 -78
bad_page.part 258 - -258
With that,
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> + } else if (bad_flags == PAGE_FLAGS_CHECK_AT_FREE) {
> + if (unlikely(page->flags & bad_flags))
> + bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag set";
> }
> #ifdef CONFIG_MEMCG
> if (unlikely(page->mem_cgroup))
> @@ -730,6 +736,17 @@ static inline int free_pages_check(struct page *page)
> bad_page(page, bad_reason, bad_flags);
> return 1;
> }
> + return 0;
> +}
> +
> +static inline int free_pages_check(struct page *page)
> +{
> + int ret = 0;
> +
> + ret = check_one_page(page, PAGE_FLAGS_CHECK_AT_FREE);
> + if (ret)
> + return ret;
> +
> page_cpupid_reset_last(page);
> if (page->flags & PAGE_FLAGS_CHECK_AT_PREP)
> page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
> @@ -1287,32 +1304,7 @@ static inline void expand(struct zone *zone, struct page *page,
> */
> static inline int check_new_page(struct page *page)
> {
> - const char *bad_reason = NULL;
> - unsigned long bad_flags = 0;
> -
> - if (unlikely(page_mapcount(page)))
> - bad_reason = "nonzero mapcount";
> - if (unlikely(page->mapping != NULL))
> - bad_reason = "non-NULL mapping";
> - if (unlikely(atomic_read(&page->_count) != 0))
> - bad_reason = "nonzero _count";
> - if (unlikely(page->flags & __PG_HWPOISON)) {
> - bad_reason = "HWPoisoned (hardware-corrupted)";
> - bad_flags = __PG_HWPOISON;
> - }
> - if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_PREP)) {
> - bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
> - bad_flags = PAGE_FLAGS_CHECK_AT_PREP;
> - }
> -#ifdef CONFIG_MEMCG
> - if (unlikely(page->mem_cgroup))
> - bad_reason = "page still charged to cgroup";
> -#endif
> - if (unlikely(bad_reason)) {
> - bad_page(page, bad_reason, bad_flags);
> - return 1;
> - }
> - return 0;
> + return check_one_page(page, PAGE_FLAGS_CHECK_AT_PREP);
> }
>
> static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
>
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