From: Andrew Morton <akpm@linux-foundation.org>
To: linux-kernel@vger.kernel.org, mingo@kernel.org, hpa@zytor.com,
a.p.zijlstra@chello.nl, torvalds@linux-foundation.org,
riel@redhat.com, akpm@linux-foundation.org, aarcange@redhat.com,
mgorman@suse.de, tglx@linutronix.de
Cc: tip-bot for Peter Zijlstra <a.p.zijlstra@chello.nl>,
linux-tip-commits@vger.kernel.org, hpa@zytor.com,
mingo@kernel.org, torvalds@linux-foundation.org, riel@redhat.com,
aarcange@redhat.com, mgorman@suse.de, tglx@linutronix.de
Subject: Re: [tip:numa/core] mm: Count the number of pages affected in change_protection()
Date: Wed, 14 Nov 2012 09:26:45 -0800 [thread overview]
Message-ID: <20121114092645.95fce74b.akpm@linux-foundation.org> (raw)
In-Reply-To: <tip-a9463d90124af069b9b58a276acc46c00054d722@git.kernel.org>
On Wed, 14 Nov 2012 06:25:56 -0800 tip-bot for Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> mm: Count the number of pages affected in change_protection()
>
> This will be used by three kinds of purposes:
>
> - to optimize mprotect()
>
> - to speed up working set scanning for working set areas that
> have not been touched
>
> - to more accurately scan per real working set
>
> No change in functionality from this patch.
Seems simple, cheap and useful.
A bit lacking in interface comments though. In particular, does the
return value (which is in units of PAGE_SIZE pages) represent the
number of pages which were inspected, or the number of pages which
actually had their permissions modified?
>From a quick look, it seems the answer is both. Or neither. If a
page's protection was written to but unaltered, that counts as a "1".
But if a pmd couldn't be locked via __pmd_trans_huge_lock(), that
counts as a "0".
Anyway, please have a think about it, and describe exactly what these
return values mean?
parent reply other threads:[~2012-11-14 17:26 UTC|newest]
Thread overview: expand[flat|nested] mbox.gz Atom feed
[parent not found: <tip-a9463d90124af069b9b58a276acc46c00054d722@git.kernel.org>]
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