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Suren Baghdasaryan 0d2ebf9c3f mm/mmap: free vm_area_struct without call_rcu in exit_mmap
call_rcu() can take a long time when callback offloading is enabled.  Its
use in the vm_area_free can cause regressions in the exit path when
multiple VMAs are being freed.

Because exit_mmap() is called only after the last mm user drops its
refcount, the page fault handlers can't be racing with it.  Any other
possible user like oom-reaper or process_mrelease are already synchronized
using mmap_lock.  Therefore exit_mmap() can free VMAs directly, without
the use of call_rcu().

Expose __vm_area_free() and use it from exit_mmap() to avoid possible
call_rcu() floods and performance regressions caused by it.

Link: https://lkml.kernel.org/r/20230227173632.3292573-33-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
History 2023-04-05 20:03:02 -07:00
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Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

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.