On Fri 07-10-16 07:27:37, Vlastimil Babka wrote: [...] > > diff --git a/mm/compaction.c b/mm/compaction.c > > index badb92bf14b4..07254a73ee32 100644 > > --- a/mm/compaction.c > > +++ b/mm/compaction.c > > @@ -834,6 +834,13 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > > page_count(page) > page_mapcount(page)) > > goto isolate_fail; > > > > + /* > > + * Only allow to migrate anonymous pages in GFP_NOFS context > > + * because those do not depend on fs locks. > > + */ > > + if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page)) > > + goto isolate_fail; > > Unless page can acquire a page_mapping between this check and migration, I > don't see a problem with allowing this. It can be become swapcache but I guess this should be OK. We do not allow to get here with GFP_NOIO and migrating swapcache pages in NOFS mode should be OK AFAICS. > But make sure you don't break kcompactd and manual compaction from /proc, as > they don't currently set cc->gfp_mask. Looks like until now it was only used > to determine direct compactor's migratetype which is irrelevant in those > contexts. OK, I see. This is really subtle. One way to go would be to provide a fake gfp_mask for them. How does the following look to you? --- diff --git a/mm/compaction.c b/mm/compaction.c index 557c165b63ad..d1d90e96ef4b 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1779,6 +1779,7 @@ static void compact_node(int nid) .mode = MIGRATE_SYNC, .ignore_skip_hint = true, .whole_zone = true, + .gfp_mask = GFP_KERNEL, }; @@ -1904,6 +1905,7 @@ static void kcompactd_do_work(pg_data_t *pgdat) .classzone_idx = pgdat->kcompactd_classzone_idx, .mode = MIGRATE_SYNC_LIGHT, .ignore_skip_hint = true, + .gfp_mask = GFP_KERNEL, }; trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order, -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>