linux-kernel - Re: [PATCH v2 1/2] mm: Move page struct poisoning to CONFIG_DEBUG_VM_PAGE_INIT

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Message-ID: <cd1fc4c6-cc86-8bf7-6aa0-b722c56057e3@microsoft.com>
Date:   Wed, 5 Sep 2018 21:22:16 +0000
From:   Pasha Tatashin <Pavel.Tatashin@...rosoft.com>
To:     Alexander Duyck <alexander.duyck@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "alexander.h.duyck@...el.com" <alexander.h.duyck@...el.com>,
        "mhocko@...e.com" <mhocko@...e.com>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v2 1/2] mm: Move page struct poisoning to
 CONFIG_DEBUG_VM_PAGE_INIT_POISON



On 9/5/18 5:13 PM, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@...el.com>
> 
> On systems with a large amount of memory it can take a significant amount
> of time to initialize all of the page structs with the PAGE_POISON_PATTERN
> value. I have seen it take over 2 minutes to initialize a system with
> over 12GB of RAM.
> 
> In order to work around the issue I had to disable CONFIG_DEBUG_VM and then
> the boot time returned to something much more reasonable as the
> arch_add_memory call completed in milliseconds versus seconds. However in
> doing that I had to disable all of the other VM debugging on the system.
> 
> Instead of keeping the value in CONFIG_DEBUG_VM I am adding a new CONFIG
> value called CONFIG_DEBUG_VM_PAGE_INIT_POISON that will control the page
> poisoning independent of the CONFIG_DEBUG_VM option.
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
> ---
>  include/linux/page-flags.h |    8 ++++++++
>  lib/Kconfig.debug          |   14 ++++++++++++++
>  mm/memblock.c              |    5 ++---
>  mm/sparse.c                |    4 +---
>  4 files changed, 25 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 74bee8cecf4c..0e95ca63375a 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -13,6 +13,7 @@
>  #include <linux/mm_types.h>
>  #include <generated/bounds.h>
>  #endif /* !__GENERATING_BOUNDS_H */
> +#include <linux/string.h>
>  
>  /*
>   * Various page->flags bits:
> @@ -162,6 +163,13 @@ static inline int PagePoisoned(const struct page *page)
>  	return page->flags == PAGE_POISON_PATTERN;
>  }
>  
> +static inline void page_init_poison(struct page *page, size_t size)
> +{
> +#ifdef CONFIG_DEBUG_VM_PAGE_INIT_POISON
> +	memset(page, PAGE_POISON_PATTERN, size);
> +#endif
> +}
> +
>  /*
>   * Page flags policies wrt compound pages
>   *
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 613316724c6a..3b1277c52fed 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -637,6 +637,20 @@ config DEBUG_VM_PGFLAGS
>  
>  	  If unsure, say N.
>  
> +config DEBUG_VM_PAGE_INIT_POISON
> +	bool "Enable early page metadata poisoning"
> +	default y
> +	depends on DEBUG_VM
> +	help
> +	  Seed the page metadata with a poison pattern to improve the
> +	  likelihood of detecting attempts to access the page prior to
> +	  initialization by the memory subsystem.
> +
> +	  This initialization can result in a longer boot time for systems
> +	  with a large amount of memory.

What happens when DEBUG_VM_PGFLAGS = y and
DEBUG_VM_PAGE_INIT_POISON = n ?

We are testing for pattern that was not set?

I think DEBUG_VM_PAGE_INIT_POISON must depend on DEBUG_VM_PGFLAGS instead.

Looks good otherwise.

Thank you,
Pavel

> +
> +	  If unsure, say Y.
> +
>  config ARCH_HAS_DEBUG_VIRTUAL
>  	bool
>  
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 237944479d25..a85315083b5a 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -1444,10 +1444,9 @@ void * __init memblock_virt_alloc_try_nid_raw(
>  
>  	ptr = memblock_virt_alloc_internal(size, align,
>  					   min_addr, max_addr, nid);
> -#ifdef CONFIG_DEBUG_VM
>  	if (ptr && size > 0)
> -		memset(ptr, PAGE_POISON_PATTERN, size);
> -#endif
> +		page_init_poison(ptr, size);
> +
>  	return ptr;
>  }
>  
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 10b07eea9a6e..67ad061f7fb8 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -696,13 +696,11 @@ int __meminit sparse_add_one_section(struct pglist_data *pgdat,
>  		goto out;
>  	}
>  
> -#ifdef CONFIG_DEBUG_VM
>  	/*
>  	 * Poison uninitialized struct pages in order to catch invalid flags
>  	 * combinations.
>  	 */
> -	memset(memmap, PAGE_POISON_PATTERN, sizeof(struct page) * PAGES_PER_SECTION);
> -#endif
> +	page_init_poison(memmap, sizeof(struct page) * PAGES_PER_SECTION);
>  
>  	section_mark_present(ms);
>  	sparse_init_one_section(ms, section_nr, memmap, usemap);
>