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Subject[PATCH v2 00/20] mm, hugetlb: remove a hugetlb_instantiation_mutex
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Without a hugetlb_instantiation_mutex, if parallel fault occur, we can
fail to allocate a hugepage, because many threads dequeue a hugepage
to handle a fault of same address. This makes reserved pool shortage
just for a little while and this cause faulting thread to get a SIGBUS
signal, although there are enough hugepages.

To solve this problem, we already have a nice solution, that is,
a hugetlb_instantiation_mutex. This blocks other threads to dive into
a fault handler. This solve the problem clearly, but it introduce
performance degradation, because it serialize all fault handling.

Now, I try to remove a hugetlb_instantiation_mutex to get rid of
performance problem reported by Davidlohr Bueso [1].

This patchset consist of 4 parts roughly.

Part 1. (1-6) Random fix and clean-up. Enhancing error handling.

These can be merged into mainline separately.

Part 2. (7-9) Protect region tracking via it's own spinlock, instead of
the hugetlb_instantiation_mutex.

Breaking dependency on the hugetlb_instantiation_mutex for
tracking a region is also needed by other approaches like as
'table mutexes', so these can be merged into mainline separately.

Part 3. (10-13) Clean-up.

IMO, these make code really simple, so these are worth to go into
mainline separately, regardless success of my approach.

Part 4. (14-20) Remove a hugetlb_instantiation_mutex.

Almost patches are just for clean-up to error handling path.
In patch 19, retry approach is implemented that if faulted thread
failed to allocate a hugepage, it continue to run a fault handler
until there is no concurrent thread having a hugepage. This causes
threads who want to get a last hugepage to be serialized, so
threads don't get a SIGBUS if enough hugepage exist.
In patch 20, remove a hugetlb_instantiation_mutex.

These patches are based on my previous patchset [2] which is now on mmotm.
In my compile testing, [2] and this patchset can be applied to
v3.11-rc4 cleanly, but, I do running test of this patchset on top of v3.10 :)

With applying these, I passed a libhugetlbfs test suite clearly which
have allocation-instantiation race test cases.

If there is a something I should consider, please let me know!
Thanks.

* Changes in v2
- Re-order patches to clear it's relationship
- sleepable object allocation(kmalloc) without holding a spinlock
(Pointed by Hillf)
- Remove vma_has_reserves, instead of vma_needs_reservation.
(Suggest by Aneesh and Naoya)
- Change a way of returning a hugepage back to reserved pool
(Suggedt by Naoya)


[1] http://lwn.net/Articles/558863/
"[PATCH] mm/hugetlb: per-vma instantiation mutexes"
[2] https://lkml.org/lkml/2013/7/22/96
"[PATCH v2 00/10] mm, hugetlb: clean-up and possible bug fix"

Joonsoo Kim (20):
mm, hugetlb: protect reserved pages when soft offlining a hugepage
mm, hugetlb: change variable name reservations to resv
mm, hugetlb: fix subpool accounting handling
mm, hugetlb: remove useless check about mapping type
mm, hugetlb: grab a page_table_lock after page_cache_release
mm, hugetlb: return a reserved page to a reserved pool if failed
mm, hugetlb: unify region structure handling
mm, hugetlb: region manipulation functions take resv_map rather
list_head
mm, hugetlb: protect region tracking via newly introduced resv_map
lock
mm, hugetlb: remove resv_map_put()
mm, hugetlb: make vma_resv_map() works for all mapping type
mm, hugetlb: remove vma_has_reserves()
mm, hugetlb: mm, hugetlb: unify chg and avoid_reserve to use_reserve
mm, hugetlb: call vma_needs_reservation before entering
alloc_huge_page()
mm, hugetlb: remove a check for return value of alloc_huge_page()
mm, hugetlb: move down outside_reserve check
mm, hugetlb: move up anon_vma_prepare()
mm, hugetlb: clean-up error handling in hugetlb_cow()
mm, hugetlb: retry if failed to allocate and there is concurrent user
mm, hugetlb: remove a hugetlb_instantiation_mutex

fs/hugetlbfs/inode.c | 16 +-
include/linux/hugetlb.h | 11 ++
mm/hugetlb.c | 419 +++++++++++++++++++++++++----------------------
3 files changed, 250 insertions(+), 196 deletions(-)

--
1.7.9.5



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