On 25.09.20 15:19, Oscar Salvador wrote: > On Wed, Sep 16, 2020 at 08:34:09PM +0200, David Hildenbrand wrote: >> __putback_isolated_page() already documents that pages will be placed to >> the tail of the freelist - this is, however, not the case for >> "order >= MAX_ORDER - 2" (see buddy_merge_likely()) - which should be >> the case for all existing users. >> >> This change affects two users: >> - free page reporting >> - page isolation, when undoing the isolation. >> >> This behavior is desireable for pages that haven't really been touched >> lately, so exactly the two users that don't actually read/write page >> content, but rather move untouched pages. >> >> The new behavior is especially desirable for memory onlining, where we >> allow allocation of newly onlined pages via undo_isolate_page_range() >> in online_pages(). Right now, we always place them to the head of the >> free list, resulting in undesireable behavior: Assume we add >> individual memory chunks via add_memory() and online them right away to >> the NORMAL zone. We create a dependency chain of unmovable allocations >> e.g., via the memmap. The memmap of the next chunk will be placed onto >> previous chunks - if the last block cannot get offlined+removed, all >> dependent ones cannot get offlined+removed. While this can already be >> observed with individual DIMMs, it's more of an issue for virtio-mem >> (and I suspect also ppc DLPAR). >> >> Note: If we observe a degradation due to the changed page isolation >> behavior (which I doubt), we can always make this configurable by the >> instance triggering undo of isolation (e.g., alloc_contig_range(), >> memory onlining, memory offlining). >> >> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >> Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> >> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> >> Cc: Michal Hocko <mhocko@xxxxxxxxxx> >> Cc: Dave Hansen <dave.hansen@xxxxxxxxx> >> Cc: Vlastimil Babka <vbabka@xxxxxxx> >> Cc: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx> >> Cc: Oscar Salvador <osalvador@xxxxxxx> >> Cc: Mike Rapoport <rppt@xxxxxxxxxx> >> Cc: Scott Cheloha <cheloha@xxxxxxxxxxxxx> >> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> >> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> > > LGTM, the only thing is the shuffe_zone topic that Wei and Vlastimil rose. > Feels a bit odd that takes precedence over something we explicitily demanded. > Thanks, yeah I'll be changing that. > With the comment Vlastimil suggested: > > Reviewed-by: Oscar Salvador <osalvador@xxxxxxx> > -- Thanks, David / dhildenb
