On Wed, Apr 14, 2021 at 07:21:42PM +0200, Vlastimil Babka wrote: > On 4/14/21 3:39 PM, Mel Gorman wrote: > > Both free_pcppages_bulk() and free_one_page() have very similar > > checks about whether a page's migratetype has changed under the > > zone lock. Use a common helper. > > > > Signed-off-by: Mel Gorman <[email protected]> > > Seems like for free_pcppages_bulk() this patch makes it check for each page on > the pcplist > - zone->nr_isolate_pageblock != 0 instead of local bool (the performance might > be the same I guess on modern cpu though) > - is_migrate_isolate(migratetype) for a migratetype obtained by > get_pcppage_migratetype() which cannot be migrate_isolate so the check is > useless. > > As such it doesn't seem a worthwhile cleanup to me considering all the other > microoptimisations? >
The patch was a preparation patch for the rest of the series to avoid code duplication and to consolidate checks together in one place to determine if they are even correct. Until zone_pcp_disable() came along, it was possible to have isolated PCP pages in the lists even though zone->nr_isolate_pageblock could be 0 during memory hot-remove so the split in free_pcppages_bulk was not necessarily correct at all times. The remaining problem is alloc_contig_pages, it does not disable PCPs so both checks are necessary. If that also disabled PCPs then check_migratetype_isolated could be deleted but the cost to alloc_contig_pages might be too high. I'll delete this patch for now because it's relatively minor and there should be other ways of keeping the code duplication down. -- Mel Gorman SUSE Labs
