Re: [PATCH v2] fs: proc: task_mmu: show page size in /proc/<pid>/numa_maps

[Rafael Aquini <aquini@redhat.com>]

On Mon, Jan 05, 2015 at 03:20:37PM -0800, Andrew Morton wrote:
> On Mon, 5 Jan 2015 17:55:05 -0500 Rafael Aquini <aquini@redhat.com> wrote:
> 
> > On Mon, Jan 05, 2015 at 01:35:00PM -0800, Andrew Morton wrote:
> > > On Mon,  5 Jan 2015 12:44:31 -0500 Rafael Aquini <aquini@redhat.com> wrote:
> > > 
> > > > This patch introduces 'kernelpagesize_kB' line element to /proc/<pid>/numa_maps
> > > > report file in order to help identifying the size of pages that are backing
> > > > memory areas mapped by a given task. This is specially useful to
> > > > help differentiating between HUGE and GIGANTIC page backed VMAs.
> > > > 
> > > > This patch is based on Dave Hansen's proposal and reviewer's follow-ups
> > > > taken from the following dicussion threads:
> > > >  * https://lkml.org/lkml/2011/9/21/454
> > > 
> > > Dave's changelog contains useful information which this one lacked.  I
> > > stole some of it.
> > > 
> > > : The output of /proc/$pid/numa_maps is in terms of number of pages like
> > > : anon=22 or dirty=54.  Here's some output:
> > > : 
> > > : 7f4680000000 default file=/hugetlb/bigfile anon=50 dirty=50 N0=50
> > > : 7f7659600000 default file=/anon_hugepage\040(deleted) anon=50 dirty=50 N0=50
> > > : 7fff8d425000 default stack anon=50 dirty=50 N0=50
> > > : Looks like we have a stack and a couple of anonymous hugetlbfs
> > > : areas page which both use the same amount of memory.  They don't.
> > > : 
> > > : The 'bigfile' uses 1GB pages and takes up ~50GB of space.  The
> > > : anon_hugepage uses 2MB pages and takes up ~100MB of space while the stack
> > > : uses normal 4k pages.  You can go over to smaps to figure out what the
> > > : page size _really_ is with KernelPageSize or MMUPageSize.  But, I think
> > > : this is a pretty nasty and counterintuitive interface as it stands.
> > > : 
> > > : This patch introduces 'kernelpagesize_kB' line element to
> > > : /proc/<pid>/numa_maps report file in order to help identifying the size of
> > > : pages that are backing memory areas mapped by a given task.  This is
> > > : specially useful to help differentiating between HUGE and GIGANTIC page
> > > : backed VMAs.
> > > : 
> > > : This patch is based on Dave Hansen's proposal and reviewer's follow-ups
> > > : taken from the following dicussion threads:
> > > :  * https://lkml.org/lkml/2011/9/21/454
> > > :  * https://lkml.org/lkml/2014/12/20/66
> > > 
> > > 
> > > > +	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
 


Cheers,
-- Rafael

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