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SubjectRe: [PATCH v3] mm/page_alloc: add a helper function to check page before alloc/free
On Tue, Sep 08, 2015 at 09:19:07PM +0200, Vlastimil Babka wrote:
> 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@163.com>
> > ---
> > 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.

OK, so let's leave as it is and see other guys' ideas. If there is any objection i will
resend with fixing the priority.

>
> 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@suse.cz>

Thanks.

>
> > + } 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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