If the total size of hugepages allocated on a system is
over half of the total memory size, commitlimit becomes
a negative number.
What happens in fs/proc/meminfo.c is this calculation:
allowed = ((totalram_pages - hugetlb_total_pages())
* sysctl_overcommit_ratio / 100) + total_swap_pages;
The problem is that hugetlb_total_pages() is larger than
totalram_pages resulting in a negative number. Since
allowed is an unsigned long the negative shows up as a
big number.
A similar calculation occurs in __vm_enough_memory() in mm/mmap.c.
A symptom of this problem is that /proc/meminfo prints a
very large CommitLimit number.
CommitLimit: 737869762947802600 kB
To reproduce the problem reserve over half of memory as hugepages.
For example "default_hugepagesz=1G hugepagesz=1G hugepages=64
Then look at /proc/meminfo "CommitLimit:" to see if it is too big.
The fix is to not subtract hugetlb_total_pages(). When hugepages
are allocated totalram_pages is decremented so there is no need to
subtract out hugetlb_total_pages() a second time.
Reported-by: Russ Anderson <rja@xxxxxxx>
Signed-off-by: Russ Anderson <rja@xxxxxxx>
---
Example of "CommitLimit:" being too big.
uv1-sys:~ # cat /proc/meminfo
MemTotal: 32395508 kB
MemFree: 32029276 kB
Buffers: 8656 kB
Cached: 89548 kB
SwapCached: 0 kB
Active: 55336 kB
Inactive: 73916 kB
Active(anon): 31220 kB
Inactive(anon): 36 kB
Active(file): 24116 kB
Inactive(file): 73880 kB
Unevictable: 0 kB
Mlocked: 0 kB
SwapTotal: 0 kB
SwapFree: 0 kB
Dirty: 1692 kB
Writeback: 0 kB
AnonPages: 31132 kB
Mapped: 15668 kB
Shmem: 152 kB
Slab: 70256 kB
SReclaimable: 17148 kB
SUnreclaim: 53108 kB
KernelStack: 6536 kB
PageTables: 3704 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 737869762947802600 kB
Committed_AS: 394044 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 713960 kB
VmallocChunk: 34325764204 kB
HardwareCorrupted: 0 kB
HugePages_Total: 32
HugePages_Free: 32
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 1048576 kB
DirectMap4k: 16384 kB
DirectMap2M: 2064384 kB
DirectMap1G: 65011712 kB
fs/proc/meminfo.c | 2 +-
mm/mmap.c | 3 +--
2 files changed, 2 insertions(+), 3 deletions(-)
Index: linux/fs/proc/meminfo.c
===================================================================
--- linux.orig/fs/proc/meminfo.c 2011-05-17 16:03:50.935658801 -0500
+++ linux/fs/proc/meminfo.c 2011-05-18 08:53:00.568784147 -0500
@@ -36,7 +36,7 @@ static int meminfo_proc_show(struct seq_
si_meminfo(&i);
si_swapinfo(&i);
committed = percpu_counter_read_positive(&vm_committed_as);
- allowed = ((totalram_pages - hugetlb_total_pages())
+ allowed = (totalram_pages
* sysctl_overcommit_ratio / 100) + total_swap_pages;
cached = global_page_state(NR_FILE_PAGES) -
Index: linux/mm/mmap.c
===================================================================
--- linux.orig/mm/mmap.c 2011-05-17 16:03:51.727658828 -0500
+++ linux/mm/mmap.c 2011-05-18 08:54:34.912222405 -0500
@@ -167,8 +167,7 @@ int __vm_enough_memory(struct mm_struct
goto error;
}
- allowed = (totalram_pages - hugetlb_total_pages())
- * sysctl_overcommit_ratio / 100;
+ allowed = totalram_pages * sysctl_overcommit_ratio / 100;
/*
* Leave the last 3% for root
*/
--
Russ Anderson, OS RAS/Partitioning Project Lead
SGI - Silicon Graphics Inc rja@xxxxxxx
--
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