lkml.org 
[lkml]   [2012]   [Jul]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 00/12] Swap-over-NFS without deadlocking V8
On Mon, Jul 02, 2012 at 08:10:51PM -0400, Eric B Munson wrote:
> On Mon, 02 Jul 2012, Mel Gorman wrote:
>
> > On Sun, Jul 01, 2012 at 01:22:54PM -0400, Eric B Munson wrote:
> > > On Fri, 29 Jun 2012, Mel Gorman wrote:
> > >
> > > > Changelog since V7
> > > > o Rebase to linux-next 20120629
> > > > o bi->page_dma instead of bi->page in intel driver
> > > > o Build fix for !CONFIG_NET (sebastian)
> > > > o Restore PF_MEMALLOC flags correctly in all cases (jlayton)
> > > >
> > > > Changelog since V6
> > > > o Rebase to linux-next 20120622
> > > >
> > > > Changelog since V5
> > > > o Rebase to v3.5-rc3
> > > >
> > > > Changelog since V4
> > > > o Catch if SOCK_MEMALLOC flag is cleared with rmem tokens (davem)
> > > >
> > > > Changelog since V3
> > > > o Rebase to 3.4-rc5
> > > > o kmap pages for writing to swap (akpm)
> > > > o Move forward declaration to reduce chance of duplication (akpm)
> > > >
> > > > Changelog since V2
> > > > o Nothing significant, just rebases. A radix tree lookup is replaced with
> > > > a linear search would be the biggest rebase artifact
> > > >
> > > > This patch series is based on top of "Swap-over-NBD without deadlocking v14"
> > > > as it depends on the same reservation of PF_MEMALLOC reserves logic.
> > > >
> > > > When a user or administrator requires swap for their application, they
> > > > create a swap partition and file, format it with mkswap and activate it with
> > > > swapon. In diskless systems this is not an option so if swap if required
> > > > then swapping over the network is considered. The two likely scenarios
> > > > are when blade servers are used as part of a cluster where the form factor
> > > > or maintenance costs do not allow the use of disks and thin clients.
> > > >
> > > > The Linux Terminal Server Project recommends the use of the Network
> > > > Block Device (NBD) for swap but this is not always an option. There is
> > > > no guarantee that the network attached storage (NAS) device is running
> > > > Linux or supports NBD. However, it is likely that it supports NFS so there
> > > > are users that want support for swapping over NFS despite any performance
> > > > concern. Some distributions currently carry patches that support swapping
> > > > over NFS but it would be preferable to support it in the mainline kernel.
> > > >
> > > > Patch 1 avoids a stream-specific deadlock that potentially affects TCP.
> > > >
> > > > Patch 2 is a small modification to SELinux to avoid using PFMEMALLOC
> > > > reserves.
> > > >
> > > > Patch 3 adds three helpers for filesystems to handle swap cache pages.
> > > > For example, page_file_mapping() returns page->mapping for
> > > > file-backed pages and the address_space of the underlying
> > > > swap file for swap cache pages.
> > > >
> > > > Patch 4 adds two address_space_operations to allow a filesystem
> > > > to pin all metadata relevant to a swapfile in memory. Upon
> > > > successful activation, the swapfile is marked SWP_FILE and
> > > > the address space operation ->direct_IO is used for writing
> > > > and ->readpage for reading in swap pages.
> > > >
> > > > Patch 5 notes that patch 3 is bolting
> > > > filesystem-specific-swapfile-support onto the side and that
> > > > the default handlers have different information to what
> > > > is available to the filesystem. This patch refactors the
> > > > code so that there are generic handlers for each of the new
> > > > address_space operations.
> > > >
> > > > Patch 6 adds an API to allow a vector of kernel addresses to be
> > > > translated to struct pages and pinned for IO.
> > > >
> > > > Patch 7 adds support for using highmem pages for swap by kmapping
> > > > the pages before calling the direct_IO handler.
> > > >
> > > > Patch 8 updates NFS to use the helpers from patch 3 where necessary.
> > > >
> > > > Patch 9 avoids setting PF_private on PG_swapcache pages within NFS.
> > > >
> > > > Patch 10 implements the new swapfile-related address_space operations
> > > > for NFS and teaches the direct IO handler how to manage
> > > > kernel addresses.
> > > >
> > > > Patch 11 prevents page allocator recursions in NFS by using GFP_NOIO
> > > > where appropriate.
> > > >
> > > > Patch 12 fixes a NULL pointer dereference that occurs when using
> > > > swap-over-NFS.
> > > >
> > > > With the patches applied, it is possible to mount a swapfile that is on an
> > > > NFS filesystem. Swap performance is not great with a swap stress test taking
> > > > roughly twice as long to complete than if the swap device was backed by NBD.
> > >
> > > To test this set I am using memory cgroups to force swap usage. I am seeing
> > > the cgroup controller killing my processes instead of using the nfs swapfile.
> > >
> >
> > How sure are you that this is not a cgroup bug? For dirty file data on some
> > kernels, cgroups can prematurely kill processes if pages are not being
> > cleaned fast enough. I would not expect the same problem for anonymous
> > pages but it's worth considering. Please also test with a normal swapfile.
> >
> > If OOM is disabled and the process hangs, try capturing a sysrq+t and
> > see where the process is stuck.
> >
>
> It looks like the problem is with cgroups, when I run without cgroups and limit
> memory on the boot command line everything works fine. To test I limited the
> machine to 1G of ram then ran several memory benchmarks with work set sizes of
> 1.5G, all completed successfully with my swap file located on an NFS share.
>
> Tested-by: Eric B Munson <emunson@mgebm.net>

Thanks a lot for testing.

--
Mel Gorman
SUSE Labs


\
 
 \ /
  Last update: 2012-07-03 11:41    [from the cache]
©2003-2011 Jasper Spaans