[PATCH] mm: fix KPF_SWAPCACHE

[PATCH] mm: fix KPF_SWAPCACHE

[Hugh Dickins]

4.10-rc1 commit 6326fec1122c ("mm: Use owner_priv bit for PageSwapCache,
valid when PageSwapBacked") aliased PG_swapcache to PG_owner_priv_1:
so /proc/kpageflags' KPF_SWAPCACHE should now be synthesized, instead
of being shown on unrelated pages which have PG_owner_priv_1 set.

Signed-off-by: Hugh Dickins <hughd@google.com>
---

 fs/proc/page.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- 4.10-rc7/fs/proc/page.c	2016-12-25 18:40:50.618454962 -0800
+++ linux/fs/proc/page.c	2017-02-07 10:28:51.019640392 -0800
@@ -173,7 +173,8 @@ u64 stable_page_flags(struct page *page)
 	u |= kpf_copy_bit(k, KPF_ACTIVE,	PG_active);
 	u |= kpf_copy_bit(k, KPF_RECLAIM,	PG_reclaim);
 
-	u |= kpf_copy_bit(k, KPF_SWAPCACHE,	PG_swapcache);
+	if (PageSwapCache(page))
+		u |= 1 << KPF_SWAPCACHE;
 	u |= kpf_copy_bit(k, KPF_SWAPBACKED,	PG_swapbacked);
 
 	u |= kpf_copy_bit(k, KPF_UNEVICTABLE,	PG_unevictable);

Re: [PATCH] mm: fix KPF_SWAPCACHE

[Nicholas Piggin]

On Tue, 7 Feb 2017 11:11:16 -0800 (PST)
Hugh Dickins <hughd@google.com> wrote:

> 4.10-rc1 commit 6326fec1122c ("mm: Use owner_priv bit for PageSwapCache,
> valid when PageSwapBacked") aliased PG_swapcache to PG_owner_priv_1:
> so /proc/kpageflags' KPF_SWAPCACHE should now be synthesized, instead
> of being shown on unrelated pages which have PG_owner_priv_1 set.
> 
> Signed-off-by: Hugh Dickins <hughd@google.com>

Thanks Hugh, this seems fine to me. We want this for 4.10, no?

Fixes: 6326fec1122c ("mm: Use owner_priv bit for PageSwapCache, valid when PageSwapBacked")
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

> ---
> 
>  fs/proc/page.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> --- 4.10-rc7/fs/proc/page.c	2016-12-25 18:40:50.618454962 -0800
> +++ linux/fs/proc/page.c	2017-02-07 10:28:51.019640392 -0800
> @@ -173,7 +173,8 @@ u64 stable_page_flags(struct page *page)
>  	u |= kpf_copy_bit(k, KPF_ACTIVE,	PG_active);
>  	u |= kpf_copy_bit(k, KPF_RECLAIM,	PG_reclaim);
>  
> -	u |= kpf_copy_bit(k, KPF_SWAPCACHE,	PG_swapcache);
> +	if (PageSwapCache(page))
> +		u |= 1 << KPF_SWAPCACHE;
>  	u |= kpf_copy_bit(k, KPF_SWAPBACKED,	PG_swapbacked);
>  
>  	u |= kpf_copy_bit(k, KPF_UNEVICTABLE,	PG_unevictable);

Re: [PATCH] mm: fix KPF_SWAPCACHE

[Hugh Dickins]

On Thu, 9 Feb 2017, Nicholas Piggin wrote:
> On Tue, 7 Feb 2017 11:11:16 -0800 (PST)
> Hugh Dickins <hughd@google.com> wrote:
> 
> > 4.10-rc1 commit 6326fec1122c ("mm: Use owner_priv bit for PageSwapCache,
> > valid when PageSwapBacked") aliased PG_swapcache to PG_owner_priv_1:
> > so /proc/kpageflags' KPF_SWAPCACHE should now be synthesized, instead
> > of being shown on unrelated pages which have PG_owner_priv_1 set.
> > 
> > Signed-off-by: Hugh Dickins <hughd@google.com>
> 
> Thanks Hugh, this seems fine to me. We want this for 4.10, no?
> 
> Fixes: 6326fec1122c ("mm: Use owner_priv bit for PageSwapCache, valid when PageSwapBacked")
> Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

Thanks Nick, yes, but don't worry: Linus jumped to it, and it's already
in 4.10 as b6789123bccb ("mm: fix KPF_SWAPCACHE in /proc/kpageflags").

Hugh