Re: [PATCH 3/3] Explicitly retry hugepage allocations

[Mel Gorman <mel@csn.ul.ie>]

On (11/04/08 16:36), Nishanth Aravamudan didst pronounce:
> Add __GFP_REPEAT to hugepage allocations. Do so to not necessitate
> userspace putting pressure on the VM by repeated echo's into
> /proc/sys/vm/nr_hugepages to grow the pool. With the previous patch to
> allow for large-order __GFP_REPEAT attempts to loop for a bit (as
> opposed to indefinitely), this increases the likelihood of getting
> hugepages when the system experiences (or recently experienced) load.
> 
> Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>

I tested the patchset on an x86_32 laptop. With the patches, it was easier to
use the proc interface to grow the hugepage pool. The following is the output
of a script that grows the pool as much as possible running on 2.6.25-rc9

Allocating hugepages test
-------------------------
Disabling OOM Killer for current test process
Starting page count: 0
Attempt 1: 57 pages Progress made with 57 pages
Attempt 2: 73 pages Progress made with 16 pages
Attempt 3: 74 pages Progress made with 1 pages
Attempt 4: 75 pages Progress made with 1 pages
Attempt 5: 77 pages Progress made with 2 pages

77 pages was the most it allocated but it took 5 attempts from userspace
to get it. With your 3 patches applied,

Allocating hugepages test
-------------------------
Disabling OOM Killer for current test process
Starting page count: 0
Attempt 1: 75 pages Progress made with 75 pages
Attempt 2: 76 pages Progress made with 1 pages
Attempt 3: 79 pages Progress made with 3 pages

And 79 pages was the most it got. Your patches were able to allocate the
bulk of possible pages on the first attempt.

Tested-by: Mel Gorman <mel@csn.ul.ie>

> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index df28c17..e13a7b2 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -199,7 +199,8 @@ static struct page *alloc_fresh_huge_page_node(int nid)
>  	struct page *page;
>  
>  	page = alloc_pages_node(nid,
> -		htlb_alloc_mask|__GFP_COMP|__GFP_THISNODE|__GFP_NOWARN,
> +		htlb_alloc_mask|__GFP_COMP|__GFP_THISNODE|
> +						__GFP_REPEAT|__GFP_NOWARN,
>  		HUGETLB_PAGE_ORDER);
>  	if (page) {
>  		if (arch_prepare_hugepage(page)) {
> @@ -294,7 +295,8 @@ static struct page *alloc_buddy_huge_page(struct vm_area_struct *vma,
>  	}
>  	spin_unlock(&hugetlb_lock);
>  
> -	page = alloc_pages(htlb_alloc_mask|__GFP_COMP|__GFP_NOWARN,
> +	page = alloc_pages(htlb_alloc_mask|__GFP_COMP|
> +					__GFP_REPEAT|__GFP_NOWARN,
>  					HUGETLB_PAGE_ORDER);
>  
>  	spin_lock(&hugetlb_lock);
> 
> -- 
> Nishanth Aravamudan <nacc@us.ibm.com>
> IBM Linux Technology Center
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab

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