Currently incorrect default hugepage pool size is reported by proc
nr_hugepages when number of pages for the default huge page size is
specified twice.
When multiple huge page sizes are supported, /proc/sys/vm/nr_hugepages
indicates the current number of pre-allocated huge pages of the default
size. Basically /proc/sys/vm/nr_hugepages displays default_hstate->
max_huge_pages and after boot time pre-allocation, max_huge_pages should
equal the number of pre-allocated pages (nr_hugepages).
Test case:
Note that this is specific to x86 architecture.
Boot the kernel with command line option 'default_hugepagesz=1G
hugepages=X hugepagesz=2M hugepages=Y hugepagesz=1G hugepages=Z'. After
boot, 'cat /proc/sys/vm/nr_hugepages' and 'sysctl -a | grep hugepages'
returns the value X. However, dmesg output shows that Z huge pages were
pre-allocated.
So, the root cause of the problem here is that the global variable
default_hstate_max_huge_pages is set if a default huge page size is
specified (directly or indirectly) on the command line. After the
command line processing in hugetlb_init, if default_hstate_max_huge_pages
is set, the value is assigned to default_hstae.max_huge_pages. However,
default_hstate.max_huge_pages may have already been set based on the
number of pre-allocated huge pages of default_hstate size.
The solution to this problem is if hstate->max_huge_pages is already set
then it should not set as a result of global max_huge_pages value.
Basically if the value of the variable hugepages is set multiple times
on a command line for a specific supported hugepagesize then proc layer
should consider the last specified value.
Signed-off-by: Vaishali Thakkar <vaishali.thakkar@xxxxxxxxxx>
---
The patch contains one line over 80 characters as I think limiting that
line to 80 characters makes code look bit ugly. But if anyone is having
issue with that then I am fine with limiting it to 80 chracters.
---
mm/hugetlb.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 06ae13e..01f2b48 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2630,8 +2630,10 @@ static int __init hugetlb_init(void)
hugetlb_add_hstate(HUGETLB_PAGE_ORDER);
}
default_hstate_idx = hstate_index(size_to_hstate(default_hstate_size));
- if (default_hstate_max_huge_pages)
- default_hstate.max_huge_pages = default_hstate_max_huge_pages;
+ if (default_hstate_max_huge_pages) {
+ if (!default_hstate.max_huge_pages)
+ default_hstate.max_huge_pages = default_hstate_max_huge_pages;
+ }
hugetlb_init_hstates();
gather_bootmem_prealloc();
--
2.1.4
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