Messages in this thread | | | Subject | Re: [PATCH 5/5] proc: export more page flags in /proc/kpageflags | From | Matt Mackall <> | Date | Tue, 28 Apr 2009 16:49:55 -0500 |
| |
On Tue, 2009-04-28 at 14:17 -0700, Andrew Morton wrote: > On Tue, 28 Apr 2009 11:11:52 -0700 > Tony Luck <tony.luck@gmail.com> wrote: > > > On Tue, Apr 28, 2009 at 1:33 AM, Wu Fengguang <fengguang.wu@intel.com> wrote: > > > 1) FAST > > > > > > It takes merely 0.2s to scan 4GB pages: > > > > > > __ __ __ __./page-types __0.02s user 0.20s system 99% cpu 0.216 total > > > > OK on a tiny system ... but sounds painful on a big > > server. 0.2s for 4G scales up to 3 minutes 25 seconds > > on a 4TB system (4TB systems were being sold two > > years ago ... so by now the high end will have moved > > up to 8TB or perhaps 16TB). > > > > Would the resulting output be anything but noise on > > a big system (a *lot* of pages can change state in > > 3 minutes)? > > > > Reading the state of all of memory in this fashion would be a somewhat > peculiar thing to do.
Not entirely. If you've got, say, a large NUMA box, it could be incredibly illustrative to see that "oh, this node is entirely dominated by SLAB allocations". Or on a smaller machine "oh, this is fragmented to hell and there's no way I'm going to get a huge page". Things you're not going to get from individual stats.
> Generally, I think that pagemap is another of those things where we've > failed on the follow-through. There's a nice and powerful interface > for inspecting the state of a process's VM, but nobody knows about it > and there are no tools for accessing it and nobody is using it.
People keep finding bugs in the thing exercising it in new ways, so I presume people are writing their own tools. My hope was that my original tools would inspire someone to take it and run with it - I really have no stomach for writing GUI tools.
However, I've recent gone and written a pretty generically useful command-line tool that hopefully will get more traction:
http://www.selenic.com/smem/
I'm expecting it to get written up on LWN shortly, so I haven't spent much time doing my own advertising.
-- http://selenic.com : development and support for Mercurial and Linux
| |