On Sun, 25 Dec 2016, Nicholas Piggin wrote:
> A page is not added to the swap cache without being swap backed,
> so PageSwapBacked mappings can use PG_owner_priv_1 for PageSwapCache.
>
> Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Yes, confirmed, Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
I checked through your migrate and memory-failure additions,
and both look correct to me. I still think that more should
be done for KPF_SWAPCACHE, to exclude the new false positives;
but as I said before, no urgency, that can be a later followup.
> Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
> ---
> include/linux/page-flags.h | 24 ++++++++++++++++--------
> include/trace/events/mmflags.h | 1 -
> mm/memory-failure.c | 4 +---
> mm/migrate.c | 14 ++++++++------
> 4 files changed, 25 insertions(+), 18 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" }, \
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 19e796d36a62..f283c7e0a2a3 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -764,12 +764,11 @@ static int me_huge_page(struct page *p, unsigned long pfn)
> */
>
> #define dirty (1UL << PG_dirty)
> -#define sc (1UL << PG_swapcache)
> +#define sc ((1UL << PG_swapcache) | (1UL << PG_swapbacked))
> #define unevict (1UL << PG_unevictable)
> #define mlock (1UL << PG_mlocked)
> #define writeback (1UL << PG_writeback)
> #define lru (1UL << PG_lru)
> -#define swapbacked (1UL << PG_swapbacked)
> #define head (1UL << PG_head)
> #define slab (1UL << PG_slab)
> #define reserved (1UL << PG_reserved)
> @@ -819,7 +818,6 @@ static struct page_state {
> #undef mlock
> #undef writeback
> #undef lru
> -#undef swapbacked
> #undef head
> #undef slab
> #undef reserved
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 0ed24b1fa77b..87f4d0f81819 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -466,13 +466,15 @@ int migrate_page_move_mapping(struct address_space *mapping,
> */
> newpage->index = page->index;
> newpage->mapping = page->mapping;
> - if (PageSwapBacked(page))
> - __SetPageSwapBacked(newpage);
> -
> get_page(newpage); /* add cache reference */
> - if (PageSwapCache(page)) {
> - SetPageSwapCache(newpage);
> - set_page_private(newpage, page_private(page));
> + if (PageSwapBacked(page)) {
> + __SetPageSwapBacked(newpage);
> + if (PageSwapCache(page)) {
> + SetPageSwapCache(newpage);
> + set_page_private(newpage, page_private(page));
> + }
> + } else {
> + VM_BUG_ON_PAGE(PageSwapCache(page), page);
> }
>
> /* Move dirty while page refs frozen and newpage not yet exposed */
> --
> 2.11.0
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