On 9/9/22 13:05, Hyeonggon Yoo wrote: >> ----8<---- >> From d6f9fbb33b908eb8162cc1f6ce7f7c970d0f285f Mon Sep 17 00:00:00 2001 >> From: Vlastimil Babka <vbabka@xxxxxxx> >> Date: Fri, 9 Sep 2022 12:03:10 +0200 >> Subject: [PATCH 2/3] mm/migrate: make isolate_movable_page() skip slab pages >> >> In the next commit we want to rearrange struct slab fields to allow a >> larger rcu_head. Afterwards, the page->mapping field will overlap >> with SLUB's "struct list_head slab_list", where the value of prev >> pointer can become LIST_POISON2, which is 0x122 + POISON_POINTER_DELTA. >> Unfortunately the bit 1 being set can confuse PageMovable() to be a >> false positive and cause a GPF as reported by lkp [1]. >> >> To fix this, make isolate_movable_page() skip pages with the PageSlab >> flag set. This is a bit tricky as we need to add memory barriers to SLAB >> and SLUB's page allocation and freeing, and their counterparts to >> isolate_movable_page(). > > Hello, I just took a quick grasp, > Is this approach okay with folio_test_anon()? Not if used on a completely random page as compaction scanners can, but relies on those being first tested for PageLRU or coming from a page table lookup etc. Not ideal huh. Well I could improve also by switching 'next' and 'slabs' field and relying on the fact that the value of LIST_POISON2 doesn't include 0x1, just 0x2.
