On Tue, 3 Mar 2020 11:37:38 +0800 "Huang, Ying" <ying.huang@xxxxxxxxx> wrote:
> From: Huang Ying <ying.huang@xxxxxxxxx>
>
> Now PageSwapBacked() is used as the helper function to check whether
> pages have been freed lazily via MADV_FREE. This isn't very obvious.
> So Dave suggested to add PageLazyFree() family helper functions to
> improve the code readability.
>
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -498,6 +498,31 @@ static __always_inline int PageKsm(struct page *page)
> TESTPAGEFLAG_FALSE(Ksm)
> #endif
>
> +/*
> + * For pages freed lazily via MADV_FREE. lazyfree pages are clean
> + * anonymous pages. They have SwapBacked flag cleared to distinguish
> + * with normal anonymous pages
> + */
> +static __always_inline int PageLazyFree(struct page *page)
> +{
> + page = compound_head(page);
> + return PageAnon(page) && !PageSwapBacked(page);
> +}
> +
> +static __always_inline void SetPageLazyFree(struct page *page)
> +{
> + VM_BUG_ON_PAGE(PageTail(page), page);
> + VM_BUG_ON_PAGE(!PageAnon(page), page);
> + ClearPageSwapBacked(page);
> +}
> +
> +static __always_inline void ClearPageLazyFree(struct page *page)
> +{
> + VM_BUG_ON_PAGE(PageTail(page), page);
> + VM_BUG_ON_PAGE(!PageAnon(page), page);
> + SetPageSwapBacked(page);
> +}
These BUG_ONs aren't present in the current code and are
unchangelogged.
And they aren't free!
before:
q:/usr/src/25> size -t mm/rmap.o mm/swap.o mm/vmscan.o
text data bss dec hex filename
41580 4211 192 45983 b39f mm/rmap.o
50684 9259 1184 61127 eec7 mm/swap.o
117728 46775 128 164631 28317 mm/vmscan.o
209992 60245 1504 271741 4257d (TOTALS)
after:
text data bss dec hex filename
42035 4299 192 46526 b5be mm/rmap.o
51091 9347 1184 61622 f0b6 mm/swap.o
118132 46775 128 165035 284ab mm/vmscan.o
211258 60421 1504 273183 42b1f (TOTALS)
ALso, if they actually trigger, Linus goes berserk.
If you have some special reason to add these assertions, please do it
as a (changelogged!) followup patch and I'll keep it as a linux-next only thing.
