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Subject[RFC PATCH 0/3] fix hugetlb page allocation stalls
Date
Allocation of hugetlb pages via sysctl or procfs can stall for minutes
or hours. A simple example on a two node system with 8GB of memory is
as follows:

echo 4096 > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages
echo 4096 > /proc/sys/vm/nr_hugepages

Obviously, both allocation attempts will fall short of their 8GB goal.
However, one or both of these commands may stall and not be interruptible.
The issues were discussed in this thread [1].

This series attempts to address the issues causing the stalls. There are
two distinct issues, and an optimization. For the reclaim and compaction
issues, suggestions were made to simply remove some existing code. However,
the impact of such changes would be hard to address. This series takes a
more conservative approach in an attempt to minimally impact existing
workloads. The question of which approach is better is debatable, hence the
RFC designation. Patches in the series address these issues:

1) Should_continue_reclaim returns true too often.
Michal Hocko suggested removing the special casing for __GFP_RETRY_MAYFAIL
in should_continue_reclaim. This does indeed address the hugetlb
allocations, but may impact other users. Hillf Danton restructured
the code in such a way to preserve much of the original semantics. Hillf's
patch also addresses hugetlb allocation issues and is included here.

2) With 1) addressed, should_compact_retry returns true too often.
Mel Gorman suggested the removal of the compaction_zonelist_suitable() call.
This routine/call was introduced by Michal Hocko for a specific use case.
Therefore, removal would likely break that use case. While examining the
reasons for compaction_withdrawn() as in [2], it appears that there are
several places where we should be using MIN_COMPACT_COSTLY_PRIORITY instead
of MIN_COMPACT_PRIORITY for costly allocations. This patch makes those
changes which also causes more appropriate should_compact_retry behavior
for hugetlb allocations.

3) This is simply an optimization of the allocation code for hugetlb pool
pages. After first __GFP_RETRY_MAYFAIL allocation failure on a node,
it drops the __GFP_RETRY_MAYFAIL flag.


[1] http://lkml.kernel.org/r/d38a095e-dc39-7e82-bb76-2c9247929f07@oracle.com
[2] http://lkml.kernel.org/r/6377c199-2b9e-e30d-a068-c304d8a3f706@oracle.com

Hillf Danton (1):
mm, reclaim: make should_continue_reclaim perform dryrun detection

Mike Kravetz (2):
mm, compaction: use MIN_COMPACT_COSTLY_PRIORITY everywhere for costly
orders
hugetlbfs: don't retry when pool page allocations start to fail

mm/compaction.c | 18 +++++++---
mm/hugetlb.c | 87 +++++++++++++++++++++++++++++++++++++++++++------
mm/vmscan.c | 28 ++++++++--------
3 files changed, 105 insertions(+), 28 deletions(-)

--
2.20.1

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