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

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Message-ID: <5498508A.4080108@linux.intel.com>
Date:	Mon, 22 Dec 2014 09:10:34 -0800
From:	Dave Hansen <dave.hansen@...ux.intel.com>
To:	Rafael Aquini <aquini@...hat.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 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.
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