Re: [PATCH v2 1/2] mm: Move page struct poisoning to CONFIG_DEBUG_VM_PAGE_INIT_POISON

Pasha Tatashin
2018-09-05T21:22:38Z

On 9/5/18 5:13 PM, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@intel.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@intel.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);
>