linux-kernel - Re: [PATCH 1/2] mm: Use owner_priv bit for PageSwapCache, valid when PageSwapBacked

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Date:   Sat, 24 Dec 2016 11:51:13 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Bob Peterson <rpeterso@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Steven Whitehouse <swhiteho@...hat.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-mm <linux-mm@...ck.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH 1/2] mm: Use owner_priv bit for PageSwapCache, valid when PageSwapBacked

Nick,
mind adding a changelog and a sign-off for these two patches?

I'd like to apply at least the first one asap, just to get as much
verification of the page flag bits as possible.

             Linus

On Wed, Dec 21, 2016 at 7:19 AM, Nicholas Piggin <npiggin@...il.com> wrote:
> ---
>  include/linux/page-flags.h     | 24 ++++++++++++++++--------
>  include/trace/events/mmflags.h |  1 -
>  2 files changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 74e4dda91238..a57c909a15e4 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -87,7 +87,6 @@ enum pageflags {
>         PG_private_2,           /* If pagecache, has fs aux data */
>         PG_writeback,           /* Page is under writeback */
>         PG_head,                /* A head page */
> -       PG_swapcache,           /* Swap page: swp_entry_t in private */
>         PG_mappedtodisk,        /* Has blocks allocated on-disk */
>         PG_reclaim,             /* To be reclaimed asap */
>         PG_swapbacked,          /* Page is backed by RAM/swap */
> @@ -110,6 +109,9 @@ enum pageflags {
>         /* Filesystems */
>         PG_checked = PG_owner_priv_1,
>
> +       /* SwapBacked */
> +       PG_swapcache = PG_owner_priv_1, /* Swap page: swp_entry_t in private */
> +
>         /* Two page bits are conscripted by FS-Cache to maintain local caching
>          * state.  These bits are set on pages belonging to the netfs's inodes
>          * when those inodes are being locally cached.
> @@ -314,7 +316,13 @@ PAGEFLAG_FALSE(HighMem)
>  #endif
>
>  #ifdef CONFIG_SWAP
> -PAGEFLAG(SwapCache, swapcache, PF_NO_COMPOUND)
> +static __always_inline int PageSwapCache(struct page *page)
> +{
> +       return PageSwapBacked(page) && test_bit(PG_swapcache, &page->flags);
> +
> +}
> +SETPAGEFLAG(SwapCache, swapcache, PF_NO_COMPOUND)
> +CLEARPAGEFLAG(SwapCache, swapcache, PF_NO_COMPOUND)
>  #else
>  PAGEFLAG_FALSE(SwapCache)
>  #endif
> @@ -701,12 +709,12 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
>   * Flags checked when a page is freed.  Pages being freed should not have
>   * these flags set.  It they are, there is a problem.
>   */
> -#define PAGE_FLAGS_CHECK_AT_FREE \
> -       (1UL << PG_lru   | 1UL << PG_locked    | \
> -        1UL << PG_private | 1UL << PG_private_2 | \
> -        1UL << PG_writeback | 1UL << PG_reserved | \
> -        1UL << PG_slab  | 1UL << PG_swapcache | 1UL << PG_active | \
> -        1UL << PG_unevictable | __PG_MLOCKED)
> +#define PAGE_FLAGS_CHECK_AT_FREE                               \
> +       (1UL << PG_lru          | 1UL << PG_locked      |       \
> +        1UL << PG_private      | 1UL << PG_private_2   |       \
> +        1UL << PG_writeback    | 1UL << PG_reserved    |       \
> +        1UL << PG_slab         | 1UL << PG_active      |       \
> +        1UL << PG_unevictable  | __PG_MLOCKED)
>
>  /*
>   * Flags checked when a page is prepped for return by the page allocator.
> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> index 5a81ab48a2fb..30c2adbdebe8 100644
> --- a/include/trace/events/mmflags.h
> +++ b/include/trace/events/mmflags.h
> @@ -95,7 +95,6 @@
>         {1UL << PG_private_2,           "private_2"     },              \
>         {1UL << PG_writeback,           "writeback"     },              \
>         {1UL << PG_head,                "head"          },              \
> -       {1UL << PG_swapcache,           "swapcache"     },              \
>         {1UL << PG_mappedtodisk,        "mappedtodisk"  },              \
>         {1UL << PG_reclaim,             "reclaim"       },              \
>         {1UL << PG_swapbacked,          "swapbacked"    },              \
> --
> 2.11.0
>