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

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Date:   Sun, 25 Dec 2016 11:00:49 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Bob Peterson <rpeterso@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        swhiteho@...hat.com, luto@...nel.org, agruenba@...hat.com,
        peterz@...radead.org, linux-mm@...ck.org,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH 1/2] mm: Use owner_priv bit for PageSwapCache, valid
 when PageSwapBacked

On Thu, 22 Dec 2016 11:55:28 -0800 (PST)
Hugh Dickins <hughd@...gle.com> wrote:

> On Thu, 22 Dec 2016, Nicholas Piggin wrote:
> 
> I agree with every word of that changelog ;)
> 
> And I'll stamp this with
> Acked-by: Hugh Dickins <hughd@...gle.com>

Thanks Hugh.
 
> The thing that Peter remembers I commented on (which 0day caught too),
> was to remove PG_swapcache from PAGE_FLAGS_CHECK_AT_FREE: you've done
> that now, so this is good.  (Note in passing: wouldn't it be good to
> add PG_waiters to PAGE_FLAGS_CHECK_AT_FREE in the 2/2?)
> 
> Though I did yesterday notice a few more problematic uses of
> PG_swapcache, which you'll probably need to refine to exclude
> other uses of PG_owner_priv_1; though no great hurry for those,
> so not necessarily in this same patch.  Do your own grep, but
> 
> fs/proc/page.c derives its KPF_SWAPCACHE from PG_swapcache,
> needs refining.
> 
> kernel/kexec_core.c says VMCOREINFO_NUMBER(PG_swapcache):
> I haven't looked into what that's about, it will probably just
> have to be commented as now including other uses of the same bit.
> 
> mm/memory-failure.c has an error_states[] table that involves
> testing PG_swapcache as "sc", but looks as if it can be changed
> to factor in "swapbacked" too.

I've added the swapbacked check to mm/memory-failure.c, the others look
like they're just dealing with bit number, so not much to do about it
really. I also just made the migration case more explicit, seeing as the
others are.

Hopefully that doesn't negate your ack because I'm adding that too.

Thanks,
Nick