On Wed, Jul 28, 2021 at 02:42:26PM +0200, Michal Hocko wrote:

On Mon 12-07-21 16:09:30, Feng Tang wrote:

quoted

The semantics of MPOL_PREFERRED_MANY is similar to MPOL_PREFERRED,
that it will first try to allocate memory from the preferred node(s),
and fallback to all nodes in system when first try fails.

Add a dedicated function for it just like 'interleave' policy.

Link: https://lore.kernel.org/r/20200630212517.308045-9-ben.widawsky@intel.com (local)
Suggested-by: Michal Hocko <mhocko@suse.com>
Co-developed-by: Ben Widawsky <redacted>
Signed-off-by: Ben Widawsky <redacted>
Signed-off-by: Feng Tang <redacted>

It would be better to squash this together with the actual user of the
function added by the next patch.

 
Ok, will do

quoted

---
 mm/mempolicy.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 17b5800b7dcc..d17bf018efcc 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c

@@ -2153,6 +2153,25 @@ static struct page *alloc_page_interleave(gfp_t gfp, unsigned order,
 	return page;
 }
 
+static struct page *alloc_page_preferred_many(gfp_t gfp, unsigned int order,
+						struct mempolicy *pol)

We likely want a node parameter to know which one we want to start with
for locality. Callers should use policy_node for that.

 
Yes, locality should be considered, something like this?

	int pnid, lnid = numa_node_id();

	if (is_nodeset(lnid, &pol->nodes))
		pnid = local_nid;
	else
		pnid = first_node(pol->nodes);

	page = __alloc_pages(((gfp | __GFP_NOWARN) & ~__GFP_DIRECT_RECLAIM),
				order, pnid, &pol->nodes);
	if (!page)
		page = __alloc_pages(gfp, order, lnid, NULL);
	return page;

quoted

+{
+	struct page *page;
+
+	/*
+	 * This is a two pass approach. The first pass will only try the
+	 * preferred nodes but skip the direct reclaim and allow the
+	 * allocation to fail, while the second pass will try all the
+	 * nodes in system.
+	 */
+	page = __alloc_pages(((gfp | __GFP_NOWARN) & ~__GFP_DIRECT_RECLAIM),
+				order, first_node(pol->nodes), &pol->nodes);

Although most users will likely have some form of GFP_*USER* here and
clearing __GFP_DIRECT_RECLAIM will put all other reclaim modifiers out
of game I think it would be better to explicitly disable some of them to
prevent from surprises. E.g. any potential __GFP_NOFAIL would be more
than surprising here. We do not have any (hopefully) but this should be
pretty cheap to exclude as we already have to modify already.

	preferred_gfp = gfp | __GFP_NOWARN;
	preferred_gfp &= ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL)

OK, will add.

Thanks,
Feng

quoted

+	if (!page)
+		page = __alloc_pages(gfp, order, numa_node_id(), NULL);
+
+	return page;
+}
+
 /**
  * alloc_pages_vma - Allocate a page for a VMA.
  * @gfp: GFP flags.
-- 
2.7.4

-- 
Michal Hocko
SUSE Labs