On 2024/11/14 15:52, Vlastimil Babka wrote:
On 11/14/24 08:44, Vlastimil Babka wrote:
On 11/14/24 07:57, Qiang Liu wrote:
It is impossible for the situation where blockpfn > end_pfn to arise,
The if statement here is not only unnecessary, but may also lead to
a misunderstanding that blockpfn > end_pfn could potentially happen.
so these unnecessary checking code should be removed.
Signed-off-by: Qiang Liu <liuq131@xxxxxxxxxxxxxxx>
I see that's since 3da0272a4c7d ("mm/compaction: correctly return failure
with bogus compound_order in strict mode")
Hm but we still have:
for (; blockpfn < end_pfn; blockpfn += stride, page += stride) {
and this advance by stride can mix up with advance by isolated, initial pfn
might not be aligned... I don't see any guarantee that the for loop will
exit with exactly blockpfn == end_pfn, it may easily advance beyond end_pfn
so we shouldn't remove the check?
Agreed.
I think that commit introduced a risk of overflow due to a bogus order
(which we read in a racy way), and once blockpfn overflows it will satisfy
<= end_pfn and might e.g. end up scanning a completely different zone?
if (blockpfn + (1UL << order) <= end_pfn) {
blockpfn += (1UL << order) - 1;
page += (1UL << order) - 1;
nr_scanned += (1UL << order) - 1;
}
We should better add back the MAX_ORDER sanity check?
---
mm/compaction.c | 6 ------
1 file changed, 6 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index a2b16b08cbbf..baeda7132252 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -682,12 +682,6 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
if (locked)
spin_unlock_irqrestore(&cc->zone->lock, flags);
- /*
- * Be careful to not go outside of the pageblock.
- */
- if (unlikely(blockpfn > end_pfn))
- blockpfn = end_pfn;
-
trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
nr_scanned, total_isolated);
