linux-kernel - Re: [PATCH] proc: task_mmu: show page size in /proc/<pid>/numa

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Message-ID: <20141222172459.GA11396@t510.redhat.com>
Date:	Mon, 22 Dec 2014 12:25:00 -0500
From:	Rafael Aquini <aquini@...hat.com>
To:	Dave Hansen <dave.hansen@...ux.intel.com>
Cc:	Johannes Weiner <hannes@...xchg.org>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, oleg@...hat.com, rientjes@...gle.com,
	linux-mm@...ck.org
Subject: Re: [PATCH] proc: task_mmu: show page size in /proc/<pid>/numa_maps

On Mon, Dec 22, 2014 at 09:10:34AM -0800, Dave Hansen wrote:
> On 12/21/2014 02:28 PM, Rafael Aquini wrote:
> >>> > > I'm fine either way, it makes the change even simpler. Also, if we
> >>> > > decide to get rid of page_size != PAGE_SIZE condition I believe we can 
> >>> > > also get rid of that "huge" hint being conditionally printed out too.
> >> > 
> >> > That would break existing users of the "huge" flag.  That makes it out
> >> > of the question, right?
> >> >
> > Yeah, but it sort of follows the same complaint Johannes did for the 
> > conditional page size printouts. If we start to print out page size
> > deliberately for each map regardless their backing pages being PAGE_SIZE 
> > long or bigger, I don't see much point on keep conditionally printing out 
> > the 'huge' hint out.
> 
> Because existing userspace might be relying on it.  If we take the
> 'huge' hint out, userspace will break.
> 
> > As I said before, I'm fine either way though I think
> > we can keep the current behaviour, and just disambiguate page sizes !=
> > PAGE_SIZE as in the current proposal.
> 
> Unless we somehow have a (really good) handle on how many apps out there
> are reading and using 'huge', I think we have to keep the existing behavior.
>
Right. I definitely don't have anything better than what I already
presented which seems beaten by your argument, already. 
Remaining question here is: should we print out 'pagesize' deliberately 
or conditionally, only to disambiguate cases where page_size != PAGE_SIZE?

Have a very nice holidays folks!
-- Rafael
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