Re: [PATCH v4 11/13] mm/mempolicy: huge-page allocation for many preferred

[Michal Hocko <mhocko@suse.com>]

Please use hugetlb prefix to make it explicit that this is hugetlb
related.

On Wed 17-03-21 11:40:08, Feng Tang wrote:
> From: Ben Widawsky <ben.widawsky@intel.com>
> 
> Implement the missing huge page allocation functionality while obeying
> the preferred node semantics.
> 
> This uses a fallback mechanism to try multiple preferred nodes first,
> and then all other nodes. It cannot use the helper function that was
> introduced because huge page allocation already has its own helpers and
> it was more LOC, and effort to try to consolidate that.
> 
> The weirdness is MPOL_PREFERRED_MANY can't be called yet because it is
> part of the UAPI we haven't yet exposed. Instead of make that define
> global, it's simply changed with the UAPI patch.
> 
> [ feng: add NOWARN flag, and skip the direct reclaim to speedup allocation
>   in some case ]
> 
> Link: https://lore.kernel.org/r/20200630212517.308045-12-ben.widawsky@intel.com
> Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
> Signed-off-by: Feng Tang <feng.tang@intel.com>
> ---
>  mm/hugetlb.c   | 26 +++++++++++++++++++++++---
>  mm/mempolicy.c |  3 ++-
>  2 files changed, 25 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 8fb42c6..9dfbfa3 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1105,7 +1105,7 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
>  				unsigned long address, int avoid_reserve,
>  				long chg)
>  {
> -	struct page *page;
> +	struct page *page = NULL;
>  	struct mempolicy *mpol;
>  	gfp_t gfp_mask;
>  	nodemask_t *nodemask;
> @@ -1126,7 +1126,17 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
>  
>  	gfp_mask = htlb_alloc_mask(h);
>  	nid = huge_node(vma, address, gfp_mask, &mpol, &nodemask);
> -	page = dequeue_huge_page_nodemask(h, gfp_mask, nid, nodemask);
> +	if (mpol->mode != MPOL_BIND && nodemask) { /* AKA MPOL_PREFERRED_MANY */

Please use MPOL_PREFERRED_MANY explicitly here.

> +		gfp_t gfp_mask1 = gfp_mask | __GFP_NOWARN;
> +
> +		gfp_mask1 &= ~__GFP_DIRECT_RECLAIM;
> +		page = dequeue_huge_page_nodemask(h,
> +				gfp_mask1, nid, nodemask);
> +		if (!page)
> +			page = dequeue_huge_page_nodemask(h, gfp_mask, nid, NULL);
> +	} else {
> +		page = dequeue_huge_page_nodemask(h, gfp_mask, nid, nodemask);
> +	}
>  	if (page && !avoid_reserve && vma_has_reserves(vma, chg)) {
>  		SetHPageRestoreReserve(page);
>  		h->resv_huge_pages--;

__GFP_DIRECT_RECLAIM handing is not needed here. dequeue_huge_page_nodemask 
only uses gfp mask to get zone and cpusets constraines. So the above
should have simply been
	if (mpol->mode == MPOL_PREFERRED_MANY) {
		page = dequeue_huge_page_nodemask(h, gfp_mask, nid, nodemask);
		if (page)
			goto got_page;
		/* fallback to all nodes */
		nodemask = NULL;
	}
	page = dequeue_huge_page_nodemask(h, gfp_mask, nid, nodemask);
got_page:
	if (page ...)

> @@ -1883,7 +1893,17 @@ struct page *alloc_buddy_huge_page_with_mpol(struct hstate *h,
>  	nodemask_t *nodemask;
>  
>  	nid = huge_node(vma, addr, gfp_mask, &mpol, &nodemask);
> -	page = alloc_surplus_huge_page(h, gfp_mask, nid, nodemask);
> +	if (mpol->mode != MPOL_BIND && nodemask) { /* AKA MPOL_PREFERRED_MANY */
> +		gfp_t gfp_mask1 = gfp_mask | __GFP_NOWARN;
> +
> +		gfp_mask1 &= ~__GFP_DIRECT_RECLAIM;
> +		page = alloc_surplus_huge_page(h,
> +				gfp_mask1, nid, nodemask);
> +		if (!page)
> +			alloc_surplus_huge_page(h, gfp_mask, nid, NULL);
> +	} else {
> +		page = alloc_surplus_huge_page(h, gfp_mask, nid, nodemask);
> +	}

And here similar
	if (mpol->mode == MPOL_PREFERRED_MANY) {
		page = alloc_surplus_huge_page(h, (gfp_mask | __GFP_NOWARN) & ~(__GFP_DIRECT_RECLAIM), nodemask);
		if (page)
			goto got_page;
		/* fallback to all nodes */
		nodemask = NULL;
	}
	page = alloc_surplus_huge_page(h, gfp_mask, nodemask);
got_page:
>  	mpol_cond_put(mpol);

You can have a dedicated gfp mask here if you prefer of course but I
calling out MPOL_PREFERRED_MANY explicitly will make the code easier to
read.

>  	return page;
-- 
Michal Hocko
SUSE Labs