linux-kernel - Re: [PATCH 1/2] mm/hugetlb: Introduce hugetlb_bad

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Message-ID: <alpine.DEB.2.10.1603230819100.16296@hxeon>
Date:	Wed, 23 Mar 2016 08:27:32 +0900 (KST)
From:	SeongJae Park <sj38.park@...il.com>
To:	Vaishali Thakkar <vaishali.thakkar@...cle.com>
cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Mike Kravetz <mike.kravetz@...cle.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Hillf Danton <hillf.zj@...baba-inc.com>,
	Michal Hocko <mhocko@...e.com>,
	Yaowei Bai <baiyaowei@...s.chinamobile.com>,
	Dominik Dingel <dingel@...ux.vnet.ibm.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 1/2] mm/hugetlb: Introduce hugetlb_bad_size

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@...cle.com>
> Cc: Mike Kravetz <mike.kravetz@...cle.com>
> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Cc: Hillf Danton <hillf.zj@...baba-inc.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Yaowei Bai <baiyaowei@...s.chinamobile.com>
> Cc: Dominik Dingel <dingel@...ux.vnet.ibm.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Paul Gortmaker <paul.gortmaker@...driver.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> ---
> The patch is having 2 checkpatch.pl 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)
> subsys_initcall(hugetlb_init);
>
> /* 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;
> 	else
> 		mhp = &parsed_hstate->max_huge_pages;
> -- 
> 2.1.4
>
> --
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