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| author | Demi Marie Obenour <demi@invisiblethingslab.com> | 2023-07-26 12:52:41 -0400 |
|---|---|---|
| committer | Juergen Gross <jgross@suse.com> | 2023-07-27 07:53:12 +0200 |
| commit | c04e9894846c663f3278a414f34416e6e45bbe68 (patch) | |
| tree | b69f437caa637263c35436466f6494145a0208f7 /Documentation | |
| parent | 58f6259b7a08f8d47d4629609703d358b042f0fd (diff) | |
| download | lwn-c04e9894846c663f3278a414f34416e6e45bbe68.tar.gz lwn-c04e9894846c663f3278a414f34416e6e45bbe68.zip | |
xen: speed up grant-table reclaim
When a grant entry is still in use by the remote domain, Linux must put
it on a deferred list. Normally, this list is very short, because
the PV network and block protocols expect the backend to unmap the grant
first. However, Qubes OS's GUI protocol is subject to the constraints
of the X Window System, and as such winds up with the frontend unmapping
the window first. As a result, the list can grow very large, resulting
in a massive memory leak and eventual VM freeze.
To partially solve this problem, make the number of entries that the VM
will attempt to free at each iteration tunable. The default is still
10, but it can be overridden via a module parameter.
This is Cc: stable because (when combined with appropriate userspace
changes) it fixes a severe performance and stability problem for Qubes
OS users.
Cc: stable@vger.kernel.org
Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20230726165354.1252-1-demi@invisiblethingslab.com
Signed-off-by: Juergen Gross <jgross@suse.com>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/ABI/testing/sysfs-module | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-module b/Documentation/ABI/testing/sysfs-module index 08886367d047..62addab47d0c 100644 --- a/Documentation/ABI/testing/sysfs-module +++ b/Documentation/ABI/testing/sysfs-module @@ -60,3 +60,14 @@ Description: Module taint flags: C staging driver module E unsigned module == ===================== + +What: /sys/module/grant_table/parameters/free_per_iteration +Date: July 2023 +KernelVersion: 6.5 but backported to all supported stable branches +Contact: Xen developer discussion <xen-devel@lists.xenproject.org> +Description: Read and write number of grant entries to attempt to free per iteration. + + Note: Future versions of Xen and Linux may provide a better + interface for controlling the rate of deferred grant reclaim + or may not need it at all. +Users: Qubes OS (https://www.qubes-os.org) |