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

From: Andrew Morton
Date: Mon Jan 05 2015 - 16:35:10 EST


On Mon, 5 Jan 2015 12:44:31 -0500 Rafael Aquini <aquini@xxxxxxxxxx> 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.

I'd complain about the patch's failure to update the documentation,
except numa_maps appears to be undocumented. Sigh. What the heck is "N0"?

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/