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. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>