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Subject[PATCH 0/3] mm,vdso: preallocate new vmas
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Linus recently pointed out[1] some of the amount of unnecessary work 
being done with the mmap_sem held. This patchset is a very initial
approach on reducing some of the contention on this lock, and moving
work outside of the critical region.

Patch 1 adds a simple helper function.

Patch 2 moves out some trivial setup logic in mlock related calls.

Patch 3 allows managing new vmas without requiring the mmap_sem for
vdsos. While it's true that there are many other scenarios where
this can be done, few are actually as straightforward as this in the
sense that we *always* end up allocating memory anyways, so there's really
no tradeoffs. For this reason I wanted to get this patch out in the open.

There are a few points to consider when preallocating vmas at the start
of system calls, such as how many new vmas (ie: callers of split_vma can
end up calling twice, depending on the mm state at that point) or the probability
that we end up merging the vma instead of having to create a new one, like the
case of brk or copy_vma. In both cases the overhead of creating and freeing
memory at every syscall's invocation might outweigh what we gain in not holding
the sem.

[1] https://lkml.org/lkml/2013/10/9/665

Thanks!

Davidlohr Bueso (3):
mm: add mlock_future_check helper
mm/mlock: prepare params outside critical region
vdso: preallocate new vmas

arch/arm/kernel/process.c | 22 +++++++++----
arch/arm64/kernel/vdso.c | 21 ++++++++++---
arch/hexagon/kernel/vdso.c | 16 +++++++---
arch/mips/kernel/vdso.c | 10 +++++-
arch/powerpc/kernel/vdso.c | 11 +++++--
arch/s390/kernel/vdso.c | 19 +++++++++---
arch/sh/kernel/vsyscall/vsyscall.c | 11 ++++++-
arch/tile/kernel/vdso.c | 13 ++++++--
arch/um/kernel/skas/mmu.c | 16 +++++++---
arch/unicore32/kernel/process.c | 17 +++++++---
arch/x86/um/vdso/vma.c | 18 ++++++++---
arch/x86/vdso/vdso32-setup.c | 16 +++++++++-
arch/x86/vdso/vma.c | 10 +++++-
include/linux/mm.h | 3 +-
kernel/events/uprobes.c | 14 +++++++--
mm/mlock.c | 18 ++++++-----
mm/mmap.c | 63 ++++++++++++++++++--------------------
17 files changed, 213 insertions(+), 85 deletions(-)

--
1.8.1.4



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