The quilt patch titled
Subject: mm/compaction: fix the total_isolated in strict mode
has been removed from the -mm tree. Its filename was
mm-compaction-fix-the-total_isolated-in-strict-mode.patch
This patch was dropped because an updated version will be issued
------------------------------------------------------
From: Qiang Liu <liuq131@xxxxxxxxxxxxxxx>
Subject: mm/compaction: fix the total_isolated in strict mode
Date: Sat, 2 Nov 2024 20:16:21 +0000
If the last cycle reads bogus compound_order() and blockpfn > end_pfn
occurs, it is possible that total_isolated will be less than nr_scanned.
In this case, strict mode should return 0, but the "if (strict &&
blockpfn < end_pfn)" statement cannot recognize this situation.
We assume that the block we are currently processing is distributed as
follows:
0 1 2 511
--------------------------------------------------
| | | |
--------------------------------------------------
Index 0 and 1 are both pages with an order of 0.
Index 2 has a bogus order (let's assume the order is 9).
When the for loop reaches index 2, it will enter the following code:
/*
* For compound pages such as THP and hugetlbfs, we can save
* potentially a lot of iterations if we skip them at once.
* The check is racy, but we can consider only valid values
* and the only danger is skipping too much.
*/
if (PageCompound(page)) {
const unsigned int order = compound_order(page);
if (blockpfn + (1UL << order) <= end_pfn) {
blockpfn += (1UL << order) - 1;
page += (1UL << order) - 1;
nr_scanned += (1UL << order) - 1;
}
goto isolate_fail;
}
After exiting the for loop:
blockpfn =basepfn+ 2+2^9 = basepfn+514;
endpfn = basepfn +512;
total_isolated = 2;
nr_scanned = 514;
/*
* Be careful to not go outside of the pageblock.
*/
if (unlikely(blockpfn > end_pfn))
blockpfn = end_pfn;
So this can happen
/*
* If strict isolation is requested by CMA then check that all the
* pages requested were isolated. If there were any failures, 0 is
* returned and CMA will fail.
*/
if (strict && blockpfn < end_pfn)
total_isolated = 0;
If processed according to the old code, it will not enter the if statement
to reset total_isolated, but the correct handling is to reset
total_isolated to 0.
Link: https://lkml.kernel.org/r/20241102201621.95291-1-liuq131@xxxxxxxxxxxxxxx
Signed-off-by: Qiang Liu <liuq131@xxxxxxxxxxxxxxx>
Cc: Laura Abbott <labbott@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/compaction.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/compaction.c~mm-compaction-fix-the-total_isolated-in-strict-mode
+++ a/mm/compaction.c
@@ -700,7 +700,7 @@ isolate_fail:
* pages requested were isolated. If there were any failures, 0 is
* returned and CMA will fail.
*/
- if (strict && blockpfn < end_pfn)
+ if (strict && (blockpfn < end_pfn || total_isolated != nr_scanned))
total_isolated = 0;
cc->total_free_scanned += nr_scanned;
_
Patches currently in -mm which might be from liuq131@xxxxxxxxxxxxxxx are
