linux-kernel - Re: [PATCH v2] fs: proc: task_mmu: show page size in /proc/<pid>/numa

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Message-Id: <20150105163146.c9576414bce83978278cb549@linux-foundation.org>
Date:	Mon, 5 Jan 2015 16:31:46 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rafael Aquini <aquini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, jweiner@...hat.com,
	dave.hansen@...ux.intel.com, rientjes@...gle.com,
	linux-mm@...ck.org
Subject: Re: [PATCH v2] fs: proc: task_mmu: show page size in
 /proc/<pid>/numa_maps

On Mon, 5 Jan 2015 19:21:35 -0500 Rafael Aquini <aquini@...hat.com> wrote:

> > > > 
> > > > 
> > > > > +	seq_printf(m, " kernelpagesize_kB=%lu", vma_kernel_pagesize(vma) >> 10);
> > > > 
> > > > This changes the format of the numa_maps file and can potentially break
> > > > existing parsers.  Please discuss.
> > 
> > ^^ ??
> >
> Sorry I overlooked it.
> 
> Parsers indeed would have to be adjusted to cope with an extra line element
> (they already have to do so, similarly, for the conditional 'huge' hint).
> Despite I don't think of it as a showstopper (as is), I think we can consider
> moving it to EOL, if its actual printout position turns out to be an issue.
>  
> 
> For instance, with this patch a numa_maps line would look like the following:
> 
>  7ff965200000 default file=/anon_hugepage\040(deleted) huge kernelpagesize_kB=2048 anon=5 dirty=5 N0=5
> 
> 
> or it could look like this, if we decide to switch kernelpagesize_kB position to EOL,
> for the sake of parsers:
> 
>  7ff965200000 default file=/anon_hugepage\040(deleted) huge anon=5 dirty=5 N0=5 kernelpagesize_kB=2048

hm, OK, numa_maps is actually a pretty complex thing: it's a
combination of `name' and `name=value'.  Some fields may be absent. 
Parsers need to fully parse each field and can't make assumptions based
on field number.

So yes, I agree that any parser which actually works is unlikely to
break due to this change.  However it's probably a bit safer to put the
new field at the end of the line.


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