Re: [PATCH] powerpc/mm: Implemented default_hugepagesz verification for powerpc

Em 2017-07-05 01:26, Aneesh Kumar K.V escreveu:

On Tuesday 04 July 2017 01:35 AM, Victor Aoqui wrote:

quoted

Implemented default hugepage size verification (default_hugepagesz=)
in order to allow allocation of defined number of pages (hugepages=)
only for supported hugepage sizes.

Signed-off-by: Victor Aoqui <redacted>
---
  arch/powerpc/mm/hugetlbpage.c | 15 +++++++++++++++
  1 file changed, 15 insertions(+)

diff --git a/arch/powerpc/mm/hugetlbpage.c 

b/arch/powerpc/mm/hugetlbpage.c
index a4f33de..464e72e 100644

--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c

@@ -797,6 +797,21 @@ static int __init hugepage_setup_sz(char *str)
  }
  __setup("hugepagesz=", hugepage_setup_sz);

+static int __init default_hugepage_setup_sz(char *str)
+{
+        unsigned long long size;
+
+        size = memparse(str, &str);
+
+        if (add_huge_page_size(size) != 0) {
+                hugetlb_bad_size();
+                pr_err("Invalid default huge page size 

specified(%llu)\n", size);
+        }
+
+        return 1;
+}
+__setup("default_hugepagesz=", default_hugepage_setup_sz);

isn't that a behavior change in what we have now ? . Right now if size
specified is not supported, we fallback to HPAGE_SIZE.

Yes, it is. However, is this a correct behavior? If we specify an 
unsupported value, for example default_hugepagesz=1M and hugepages=1000, 
1M will be ignored and 1000 pages of 16M (arch default) will be 
allocated. This could lead to non-expected out of of memory/performance 
issue.

mm/hugetlb.c

if (!size_to_hstate(default_hstate_size)) {
	default_hstate_size = HPAGE_SIZE;
	if (!size_to_hstate(default_hstate_size))
		hugetlb_add_hstate(HUGETLB_PAGE_ORDER);
}

quoted

+
  struct kmem_cache *hugepte_cache;
  static int __init hugetlbpage_init(void)
  {

Even if we want to do this, this should be done in generic code and
should not be powerpc specific

The verification of supported powerpc hugepage size (hugepagesz=) is 
being performed on add_huge_page_size(), which is currently defined in 
arch/powerpc/mm/hugetlbpage.c. I think it makes more sense to implement 
default_hugepagesz= verification on arch/powerpc, don't you think?

-aneesh