linux-kernel - Re: [PATCH v6 2/5] mm,compaction: Let isolate_migratepages

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Date:   Tue, 23 Mar 2021 11:49:03 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Muchun Song <songmuchun@...edance.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/5] mm,compaction: Let
 isolate_migratepages_{range,block} return error codes

On Fri, Mar 19, 2021 at 02:20:01PM +0100, Oscar Salvador wrote:
> Currently, isolate_migratepages_{range,block} and their callers use
> a pfn == 0 vs pfn != 0 scheme to let the caller know whether there was
> any error during isolation.
> This does not work as soon as we need to start reporting different error
> codes and make sure we pass them down the chain, so they are properly
> interpreted by functions like e.g: alloc_contig_range.
> 
> Let us rework isolate_migratepages_{range,block} so we can report error
> codes.
> Since isolate_migratepages_block will stop returning the next pfn to be
> scanned, we reuse the cc->migrate_pfn field to keep track of that.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Hi Andrew,

I realized a missed place wrt. error handling.
could you squash this on top?

diff --git a/mm/compaction.c b/mm/compaction.c
index cd090a675321..9b989fc3168d 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -809,6 +809,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 	bool skip_on_failure = false;
 	unsigned long next_skip_pfn = 0;
 	bool skip_updated = false;
+	int ret = 0;
 
 	cc->migrate_pfn = low_pfn;
 
@@ -877,8 +878,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 
 			if (fatal_signal_pending(current)) {
 				cc->contended = true;
+				ret = -EINTR;
 
-				low_pfn = 0;
 				goto fatal_pending;
 			}
 
@@ -1134,7 +1135,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 
 	cc->migrate_pfn = low_pfn;
 
-	return 0;
+	return ret;
 }


Thanks a lot

-- 
Oscar Salvador
SUSE L3