Re: [PATCH 0/5] fix up /proc/$pid/smaps to not split huge pages

Andrea Arcangeli
2011-02-15T17:02:00Z

On Tue, Feb 15, 2011 at 11:55:10AM -0500, Eric B Munson wrote:
> I am noticing in smaps that KernelPageSize is wrong of areas
> that have been merged into THP. For instance:
>
> 7ff852a00000-7ff852c00000 rw-p 00000000 00:00 0
> Size: 2048 kB
> Rss: 2048 kB
> Pss: 2048 kB
> Shared_Clean: 0 kB
> Shared_Dirty: 0 kB
> Private_Clean: 0 kB
> Private_Dirty: 2048 kB
> Referenced: 2048 kB
> Anonymous: 2048 kB
> AnonHugePages: 2048 kB
> Swap: 0 kB
> KernelPageSize: 4 kB
> MMUPageSize: 4 kB
> Locked: 0 kB
>
> The entire mapping is contained in a THP but the
> KernelPageSize shows 4kb. For cases where the mapping might
> have mixed page sizes this may be okay, but for this
> particular mapping the 4kb page size is wrong.

I'm not sure this is a bug, if the mapping grows it may become 4096k
but the new pages may be 4k. There's no such thing as a
vma_mmu_pagesize in terms of hugepages because we support graceful
fallback and collapse/split on the fly without altering the vma. So I
think 4k is correct here.