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authorMark Johnston <markj@FreeBSD.org>2022-10-05 19:12:46 +0000
committerMark Johnston <markj@FreeBSD.org>2022-10-05 19:12:46 +0000
commit2c9dc2384f85a4ccc44a79b349f4fb0253a2f254 (patch)
tree3dc99d19e23f804c2906d1ebff0f37b8685f4bb5 /targets/pseudo/gcc
parent070e8d36d9b3edee4d8b36cdf9745b9af239dce6 (diff)
downloadsrc-2c9dc2384f85a4ccc44a79b349f4fb0253a2f254.tar.gz
src-2c9dc2384f85a4ccc44a79b349f4fb0253a2f254.zip
vm_page: Fix a logic error in the handling of PQ_ACTIVE operations
As an optimization, vm_page_activate() avoids requeuing a page that's already in the active queue. A page's location in the active queue is mostly unimportant. When a page is unwired and placed back in the page queues, vm_page_unwire() avoids moving pages out of PQ_ACTIVE to honour the request, the idea being that they're likely mapped and so will simply get bounced back in to PQ_ACTIVE during a queue scan. In both cases, if the page was logically in PQ_ACTIVE but had not yet been physically enqueued (i.e., the page is in a per-CPU batch), we would end up clearing PGA_REQUEUE from the page. Then, batch processing would ignore the page, so it would end up unwired and not in any queues. This can arise, for example, when a page is allocated and then vm_page_activate() is called multiple times in quick succession. The result is that the page is hidden from the page daemon, so while it will be freed when its VM object is destroyed, it cannot be reclaimed under memory pressure. Fix the bug: when checking if a page is in PQ_ACTIVE, only perform the optimization if the page is physically enqueued. PR: 256507 Fixes: f3f38e2580f1 ("Start implementing queue state updates using fcmpset loops.") Reviewed by: alc, kib MFC after: 1 week Sponsored by: E-CARD Ltd. Sponsored by: Klara, Inc. Differential Revision: https://reviews.freebsd.org/D36839
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