linux-kernel - Re: [PATCH 1/3] mm, numa: rework do_pages

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Date:   Fri, 5 Jan 2018 12:41:22 -0600 (CST)
From:   Christopher Lameter <cl@...ux.com>
To:     Michal Hocko <mhocko@...nel.org>
cc:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Zi Yan <zi.yan@...rutgers.edu>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrea Reale <ar@...ux.vnet.ibm.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] mm, numa: rework do_pages_move

On Fri, 5 Jan 2018, Michal Hocko wrote:

> I believe there should be some cap on the number of pages. We shouldn't
> keep it held for million of pages if all of them are moved to the same
> node. I would really like to postpone that to later unless it causes
> some noticeable regressions because this would complicate the code
> further and I am not sure this is all worth it.

Attached a patch to make the code more readable.

Also why are you migrating the pages on pagelist if a
add_page_for_migration() fails? One could simply update
the status in user space and continue.


Index: linux/mm/migrate.c
===================================================================
--- linux.orig/mm/migrate.c
+++ linux/mm/migrate.c
@@ -1584,16 +1584,20 @@ static int do_pages_move(struct mm_struc
 		if (!node_isset(node, task_nodes))
 			goto out_flush;

-		if (current_node == NUMA_NO_NODE) {
-			current_node = node;
-			start = i;
-		} else if (node != current_node) {
-			err = do_move_pages_to_node(mm, &pagelist, current_node);
-			if (err)
-				goto out;
-			err = store_status(status, start, current_node, i - start);
-			if (err)
-				goto out;
+		if (node != current_node) {
+
+			if (current_node != NUMA_NO_NODE) {
+
+				/* Move the pages to current_node */
+				err = do_move_pages_to_node(mm, &pagelist, current_node);
+				if (err)
+					goto out;
+
+				err = store_status(status, start, current_node, i - start);
+				if (err)
+					goto out;
+			}
+
 			start = i;
 			current_node = node;
 		}
@@ -1607,6 +1611,10 @@ static int do_pages_move(struct mm_struc
 		if (!err)
 			continue;

+		/*
+		 * Failure to isolate a page so flush the pages on
+		 * pagelist after storing status and continue.
+		 */
 		err = store_status(status, i, err, 1);
 		if (err)
 			goto out_flush;
@@ -1614,6 +1622,7 @@ static int do_pages_move(struct mm_struc
 		err = do_move_pages_to_node(mm, &pagelist, current_node);
 		if (err)
 			goto out;
+
 		if (i > start) {
 			err = store_status(status, start, current_node, i - start);
 			if (err)