On Fri, Feb 20, 2015 at 07:56:15PM -0800, Hugh Dickins wrote:
> Commit 07a427884348 ("mm: shmem: avoid atomic operation during
> shmem_getpage_gfp") rightly replaced one instance of SetPageSwapBacked
> by __SetPageSwapBacked, pointing out that the newly allocated page is
> not yet visible to other users (except speculative get_page_unless_zero-
> ers, who may not update page flags before their further checks).
>
> That was part of a series in which Mel was focused on tmpfs profiles:
> but almost all SetPageSwapBacked uses can be so optimized, with the
> same justification. And remove the ClearPageSwapBacked from
> read_swap_cache_async()'s and zswap_get_swap_cache_page()'s error
> paths: it's not an error to free a page with PG_swapbacked set.
>
> (There's probably scope for further __SetPageFlags in other places,
> but SwapBacked is the one I'm interested in at the moment.)
>
> Signed-off-by: Hugh Dickins <hu...@google.com>
> ---
> mm/migrate.c | 6 +++---
> mm/rmap.c | 2 +-
> mm/shmem.c | 4 ++--
> mm/swap_state.c | 3 +--
> mm/zswap.c | 3 +--
> 5 files changed, 8 insertions(+), 10 deletions(-)
>
> <SNIP>
> --- thpfs.orig/mm/shmem.c 2015-02-08 18:54:22.000000000 -0800
> +++ thpfs/mm/shmem.c 2015-02-20 19:33:35.676074594 -0800
> @@ -987,8 +987,8 @@ static int shmem_replace_page(struct pag
> flush_dcache_page(newpage);
>
> __set_page_locked(newpage);
> + __SetPageSwapBacked(newpage);
> SetPageUptodate(newpage);
> - SetPageSwapBacked(newpage);
> set_page_private(newpage, swap_index);
> SetPageSwapCache(newpage);
>
It's clear why you did this but ...
> @@ -1177,8 +1177,8 @@ repeat:
> goto decused;
> }
>
> - __SetPageSwapBacked(page);
> __set_page_locked(page);
> + __SetPageSwapBacked(page);
> if (sgp == SGP_WRITE)
> __SetPageReferenced(page);
>
It's less clear why this was necessary. I don't think it causes any
problems though so
Reviewed-by: Mel Gorman <mgor...@suse.de>
--
Mel Gorman
SUSE Labs
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