Messages in this thread | | | From | "Wang, Yalin" <> | Date | Thu, 4 Dec 2014 14:10:53 +0800 | Subject | RE: [RFC V2] mm:add zero_page _mapcount when mapped into user space |
| |
> -----Original Message----- > From: Kirill A. Shutemov [mailto:kirill@shutemov.name] > Sent: Tuesday, December 02, 2014 7:30 PM > To: Wang, Yalin > Cc: 'linux-kernel@vger.kernel.org'; 'linux-mm@kvack.org'; 'linux-arm- > kernel@lists.infradead.org' > Subject: Re: [RFC V2] mm:add zero_page _mapcount when mapped into user > space > > On Tue, Dec 02, 2014 at 05:27:36PM +0800, Wang, Yalin wrote: > > This patch add/dec zero_page's _mapcount to make sure the mapcount is > > correct for zero_page, so that when read from /proc/kpagecount, > > zero_page's mapcount is also correct, userspace process like procrank > > can calculate PSS correctly. > > I don't have specific code path to point to, but I would expect zero page > with non-zero mapcount would cause a problem with rmap. > > How do you test the change? > I just test it to see the mapcount from /proc/pid/pagemap and /proc/kpagecount , It works well, The problem is that when I see /proc/pid/smaps , The Rss / Pss don't calculate zero_page map, Because smaps_pte_entry() --> vm_normal_page( ), Will return NULL for zero_page,
But when userspace process cat /proc/pid/pagemap , It will see zero_page mapped, And will treat as Rss , This is weird, should we also omit zero_page in /proc/pid/pagemap ? Or add zero_page as Rss in /proc/pid/smaps ?
I think we should add zero_page into Rss , Because it is really mapped into userspace address space. And will let userspace memory analysis more accurate .
Thanks
| |