linux-kernel - [PATCH v4 01/13] mm/mempolicy: Add comment for missing LOCAL

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Date:   Wed, 17 Mar 2021 11:39:58 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dave Hansen <dave.hansen@...el.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Feng Tang <feng.tang@...el.com>
Subject: [PATCH v4 01/13] mm/mempolicy: Add comment for missing LOCAL

From: Ben Widawsky <ben.widawsky@...el.com>

MPOL_LOCAL is a bit weird because it is simply a different name for an
existing behavior (preferred policy with no node mask). It has been this
way since it was added here:
commit 479e2802d09f ("mm: mempolicy: Make MPOL_LOCAL a real policy")

It is so similar to MPOL_PREFERRED in fact that when the policy is
created in mpol_new, the mode is set as PREFERRED, and an internal state
representing LOCAL doesn't exist.

To prevent future explorers from scratching their head as to why
MPOL_LOCAL isn't defined in the mpol_ops table, add a small comment
explaining the situations.

v2:
Change comment to refer to mpol_new (Michal)

Link: https://lore.kernel.org/r/20200630212517.308045-2-ben.widawsky@intel.com
Acked-by: Michal Hocko <mhocko@...e.com>
Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>
Signed-off-by: Feng Tang <feng.tang@...el.com>
---
 mm/mempolicy.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index ab51132..4193566 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -427,6 +427,7 @@ static const struct mempolicy_operations mpol_ops[MPOL_MAX] = {
 		.create = mpol_new_bind,
 		.rebind = mpol_rebind_nodemask,
 	},
+	/* [MPOL_LOCAL] - see mpol_new() */
 };
 
 static int migrate_page_add(struct page *page, struct list_head *pagelist,
-- 
2.7.4