Re: +mm-show_mem-suppress-page-counts-in-non-blockable-contexts.patch added to-mm tree

[Michal Hocko]

On Thu 28-02-13 15:10:25, Andrew Morton wrote:
[...]
> From: David Rientjes <rientjes@xxxxxxxxxx>
> Subject: mm, show_mem: suppress page counts in non-blockable contexts
> 
> On large systems with a lot of memory, walking all RAM to determine page
> types may take a half second or even more.
> 
> In non-blockable contexts, the page allocator will emit a page allocation
> failure warning unless __GFP_NOWARN is specified.  In such contexts, irqs
> are typically disabled and such a lengthy delay may result in soft
> lockups.

I have already asked about it in the original thread but didn't get any
answer. How can we get a soft lockup when all implementations of show_mem
call touch_nmi_watchdog?

I do agree with the change but the above justification seems misleading.
Can we just remove the information because it is costly and doesn't give
us anything relevant to debug allocation failures?

> To fix this, suppress the page walk in such contexts when printing the
> page allocation failure warning.
> 
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>
> Cc: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
> 
>  arch/arm/mm/init.c       |    3 +++
>  arch/ia64/mm/contig.c    |    2 ++
>  arch/ia64/mm/discontig.c |    2 ++
>  arch/parisc/mm/init.c    |    2 ++
>  arch/unicore32/mm/init.c |    3 +++
>  include/linux/mm.h       |    3 ++-
>  lib/show_mem.c           |    3 +++
>  mm/page_alloc.c          |    7 +++++++
>  8 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff -puN arch/arm/mm/init.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts arch/arm/mm/init.c
> --- a/arch/arm/mm/init.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts
> +++ a/arch/arm/mm/init.c
> @@ -99,6 +99,9 @@ void show_mem(unsigned int filter)
>  	printk("Mem-info:\n");
>  	show_free_areas(filter);
>  
> +	if (filter & SHOW_MEM_FILTER_PAGE_COUNT)
> +		return;
> +
>  	for_each_bank (i, mi) {
>  		struct membank *bank = &mi->bank[i];
>  		unsigned int pfn1, pfn2;
> diff -puN arch/ia64/mm/contig.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts arch/ia64/mm/contig.c
> --- a/arch/ia64/mm/contig.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts
> +++ a/arch/ia64/mm/contig.c
> @@ -47,6 +47,8 @@ void show_mem(unsigned int filter)
>  	printk(KERN_INFO "Mem-info:\n");
>  	show_free_areas(filter);
>  	printk(KERN_INFO "Node memory in pages:\n");
> +	if (filter & SHOW_MEM_FILTER_PAGE_COUNT)
> +		return;
>  	for_each_online_pgdat(pgdat) {
>  		unsigned long present;
>  		unsigned long flags;
> diff -puN arch/ia64/mm/discontig.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts arch/ia64/mm/discontig.c
> --- a/arch/ia64/mm/discontig.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts
> +++ a/arch/ia64/mm/discontig.c
> @@ -623,6 +623,8 @@ void show_mem(unsigned int filter)
>  
>  	printk(KERN_INFO "Mem-info:\n");
>  	show_free_areas(filter);
> +	if (filter & SHOW_MEM_FILTER_PAGE_COUNT)
> +		return;
>  	printk(KERN_INFO "Node memory in pages:\n");
>  	for_each_online_pgdat(pgdat) {
>  		unsigned long present;
> diff -puN arch/parisc/mm/init.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts arch/parisc/mm/init.c
> --- a/arch/parisc/mm/init.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts
> +++ a/arch/parisc/mm/init.c
> @@ -697,6 +697,8 @@ void show_mem(unsigned int filter)
>  
>  	printk(KERN_INFO "Mem-info:\n");
>  	show_free_areas(filter);
> +	if (filter & SHOW_MEM_FILTER_PAGE_COUNT)
> +		return;
>  #ifndef CONFIG_DISCONTIGMEM
>  	i = max_mapnr;
>  	while (i-- > 0) {
> diff -puN arch/unicore32/mm/init.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts arch/unicore32/mm/init.c
> --- a/arch/unicore32/mm/init.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts
> +++ a/arch/unicore32/mm/init.c
> @@ -66,6 +66,9 @@ void show_mem(unsigned int filter)
>  	printk(KERN_DEFAULT "Mem-info:\n");
>  	show_free_areas(filter);
>  
> +	if (filter & SHOW_MEM_FILTER_PAGE_COUNT)
> +		return;
> +
>  	for_each_bank(i, mi) {
>  		struct membank *bank = &mi->bank[i];
>  		unsigned int pfn1, pfn2;
> diff -puN include/linux/mm.h~mm-show_mem-suppress-page-counts-in-non-blockable-contexts include/linux/mm.h
> --- a/include/linux/mm.h~mm-show_mem-suppress-page-counts-in-non-blockable-contexts
> +++ a/include/linux/mm.h
> @@ -900,7 +900,8 @@ extern void pagefault_out_of_memory(void
>   * Flags passed to show_mem() and show_free_areas() to suppress output in
>   * various contexts.
>   */
> -#define SHOW_MEM_FILTER_NODES	(0x0001u)	/* filter disallowed nodes */
> +#define SHOW_MEM_FILTER_NODES		(0x0001u)	/* disallowed nodes */
> +#define SHOW_MEM_FILTER_PAGE_COUNT	(0x0002u)	/* page type count */
>  
>  extern void show_free_areas(unsigned int flags);
>  extern bool skip_free_areas_node(unsigned int flags, int nid);
> diff -puN lib/show_mem.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts lib/show_mem.c
> --- a/lib/show_mem.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts
> +++ a/lib/show_mem.c
> @@ -18,6 +18,9 @@ void show_mem(unsigned int filter)
>  	printk("Mem-Info:\n");
>  	show_free_areas(filter);
>  
> +	if (filter & SHOW_MEM_FILTER_PAGE_COUNT)
> +		return;
> +
>  	for_each_online_pgdat(pgdat) {
>  		unsigned long i, flags;
>  
> diff -puN mm/page_alloc.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts mm/page_alloc.c
> --- a/mm/page_alloc.c~mm-show_mem-suppress-page-counts-in-non-blockable-contexts
> +++ a/mm/page_alloc.c
> @@ -2009,6 +2009,13 @@ void warn_alloc_failed(gfp_t gfp_mask, i
>  		return;
>  
>  	/*
> +	 * Walking all memory to count page types is very expensive and should
> +	 * be inhibited in non-blockable contexts.
> +	 */
> +	if (!(gfp_mask & __GFP_WAIT))
> +		filter |= SHOW_MEM_FILTER_PAGE_COUNT;
> +
> +	/*
>  	 * This documents exceptions given to allocations in certain
>  	 * contexts that are allowed to allocate outside current's set
>  	 * of allowed nodes.
> _
> 
> Patches currently in -mm which might be from rientjes@xxxxxxxxxx are
> 
> origin.patch
> mm-show_mem-suppress-page-counts-in-non-blockable-contexts.patch
> mm-dmapoolc-fix-null-dev-in-dma_pool_create.patch
> 

-- 
Michal Hocko
SUSE Labs
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