Fork of reMarkable kernel https://github.com/reMarkable/linux
b6bb981149
By default, vmpressure events are not pass-through, i.e. they propagate up through the memcg hierarchy until an event notifier is found for any threshold level. This presents a difficulty when a thread waiting on a read(2) for a vmpressure event cannot distinguish between local memory pressure and memory pressure in a descendant memcg, especially when that thread may not control the memcg hierarchy. Consider a user-controlled child memcg with a smaller limit than a top-level memcg controlled by the "Activity Manager" specified in Documentation/cgroup-v1/memory.txt. It may register for memory pressure notification for descendant memcgs to make a policy decision: oom kill a low priority job, increase the limit, decrease other limits, etc. If it registers for memory pressure notification on the top-level memcg, it currently cannot distinguish between memory pressure in its own memcg or a descendant memcg, which is user-controlled. Conversely, if a user registers for memory pressure notification on their own descendant memcg, the Activity Manager does not receive any pressure notification for that child memcg hierarchy. Vmpressure events are not received for ancestor memcgs if the memcg experiencing pressure have notifiers registered, perhaps outside the knowledge of the thread waiting on read(2) at the top level. Both of these are consequences of vmpressure notification not being pass-through. This implements a pass-through behavior for vmpressure events. When writing to control.event_control, vmpressure event handlers may optionally specify a mode. There are two new modes: - "hierarchy": always propagate memory pressure events up the hierarchy regardless if descendant memcgs have their own notifiers registered, and - "local": only receive notifications when the memcg for which the event is registered experiences memory pressure. Of course, processes may register for one notification of "low,local", for example, and another for "low". If no mode is specified, the current behavior is maintained for backwards compatibility. See the change to Documentation/cgroup-v1/memory.txt for full specification. [dan.carpenter@oracle.com: free the same pointer we allocated] Link: http://lkml.kernel.org/r/20170613191820.GA20003@elgon.mountain Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1705311421320.8946@chino.kir.corp.google.com Signed-off-by: David Rientjes <rientjes@google.com> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Minchan Kim <minchan@kernel.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Anton Vorontsov <anton@enomsg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.