On 17.05.23 18:15, Khalid Aziz wrote:
Pages pinned in memory through extra refcounts can not be migrated. Currently as isolate_migratepages_block() scans pages for compaction, it skips any pinned anonymous pages. All non-migratable pages should be skipped and not just the anonymous pinned pages. This patch adds a check for extra refcounts on a page to determine if the page can be migrated. This was seen as a real issue on a customer workload where a large number of pages were pinned by vfio on the host and any attempts to allocate hugepages resulted in significant amount of cpu time spent in either direct compaction or in kcompactd scanning vfio pinned pages over and over again that can not be migrated.
How will this change affect alloc_contig_range(), such as used for CMA allocations or virtio-mem? alloc_contig_range() ends up calling isolate_migratepages_range() -> isolate_migratepages_block().
We don't want to fail early in case there is a short-term pin that might go away any moment after we isolated ... that will make the situation worse for these use cases, especially if MIGRATE_CMA or ZONE_MOVABLE is involved.
-- Thanks, David / dhildenb
