Re: [PATCH 1/2] mm/hugetlb: Introduce hugetlb_bad_size

From: SeongJae Park
Date: Tue Mar 22 2016 - 19:35:21 EST

Hello Vaishali,

The patch looks good to me. However, I have few trivial questions.

On Tue, 22 Mar 2016, Vaishali Thakkar wrote:

When any unsupported hugepage size is specified, 'hugepagesz=' and
'hugepages=' should be ignored during command line parsing until any
supported hugepage size is found. But currently incorrect number of
hugepages are allocated when unsupported size is specified as it fails
to ignore the 'hugepages=' command.

Test case:

Note that this is specific to x86 architecture.

Boot the kernel with command line option 'hugepagesz=256M hugepages=X'.
After boot, dmesg output shows that X number of hugepages of the size 2M
is pre-allocated instead of 0.

So, to handle such command line options, introduce new routine
hugetlb_bad_size. The routine hugetlb_bad_size sets the global variable
parsed_valid_hugepagesz. We are using parsed_valid_hugepagesz to save the
state when unsupported hugepagesize is found so that we can ignore the
'hugepages=' parameters after that and then reset the variable when
supported hugepage size is found.

The routine hugetlb_bad_size can be called while setting 'hugepagesz='
parameter in an architecture specific code.

Signed-off-by: Vaishali Thakkar <vaishali.thakkar@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Yaowei Bai <baiyaowei@xxxxxxxxxxxxxxxxxxxx>
Cc: Dominik Dingel <dingel@xxxxxxxxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
The patch is having 2 warnings. I have just followed
the current code to maintain consistency. If we decide to silent
these warnings then may be we should silent those warnings as well.
I am fine with any option whichever works best for everyone else.
include/linux/hugetlb.h | 1 +
mm/hugetlb.c | 14 +++++++++++++-
2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 7d953c2..e44c578 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -338,6 +338,7 @@ int huge_add_to_page_cache(struct page *page, struct address_space *mapping,
/* arch callback */
int __init alloc_bootmem_huge_page(struct hstate *h);

+void __init hugetlb_bad_size(void);
void __init hugetlb_add_hstate(unsigned order);
struct hstate *size_to_hstate(unsigned long size);

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 06058ea..44fae6a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -51,6 +51,7 @@ __initdata LIST_HEAD(huge_boot_pages);
static struct hstate * __initdata parsed_hstate;
static unsigned long __initdata default_hstate_max_huge_pages;
static unsigned long __initdata default_hstate_size;
+static bool __initdata parsed_valid_hugepagesz = true;

* Protects updates to hugepage_freelists, hugepage_activelist, nr_huge_pages,
@@ -2659,6 +2660,11 @@ static int __init hugetlb_init(void)

/* Should be called on processing a hugepagesz=... option */
+void __init hugetlb_bad_size(void)
+ parsed_valid_hugepagesz = false;
void __init hugetlb_add_hstate(unsigned int order)
struct hstate *h;
@@ -2691,11 +2697,17 @@ static int __init hugetlb_nrpages_setup(char *s)
unsigned long *mhp;
static unsigned long *last_mhp;

+ if (!parsed_valid_hugepagesz) {
+ pr_warn("hugepages = %s preceded by "
+ "an unsupported hugepagesz, ignoring\n", s);

How about concatenating the format string? `CodingStyle` now suggests to
_never_ break every user-visible strings.

+ parsed_valid_hugepagesz = true;
+ return 1;
+ }
* !hugetlb_max_hstate means we haven't parsed a hugepagesz= parameter yet,
* so this hugepages= parameter goes to the "default hstate".
- if (!hugetlb_max_hstate)
+ else if (!hugetlb_max_hstate)

Because the upper `if` statement will do `return`, above change looks not
significantly necessary. Is this intended?

mhp = &default_hstate_max_huge_pages;
mhp = &parsed_hstate->max_huge_pages;

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