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From:   Ben Widawsky <ben.widawsky@intel.com>
To:     linux-mm <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Ben Widawsky <ben.widawsky@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Michal Hocko <mhocko@kernel.org>,
        Michal Hocko <mhocko@suse.com>, linux-kernel@vger.kernel.org
Subject: [PATCH 01/12] mm/mempolicy: Add comment for missing LOCAL
Date:   Fri, 30 Oct 2020 12:02:27 -0700
Message-Id: <20201030190238.306764-2-ben.widawsky@intel.com>
In-Reply-To: <20201030190238.306764-1-ben.widawsky@intel.com>
References: <20201030190238.306764-1-ben.widawsky@intel.com>
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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@suse.com>
Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
---
 mm/mempolicy.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 3fde772ef5ef..e24f0133ff1f 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,
-- 
2.29.2