[lkml]   [2020]   [Sep]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH RFC 2/4] mm/page_alloc: place pages to tail in __putback_isolated_page()
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 <>
> Cc: Alexander Duyck <>
> Cc: Mel Gorman <>
> Cc: Michal Hocko <>
> Cc: Dave Hansen <>
> Cc: Vlastimil Babka <>
> Cc: Wei Yang <>
> Cc: Oscar Salvador <>
> Cc: Mike Rapoport <>
> Cc: Scott Cheloha <>
> Cc: Michael Ellerman <>
> Signed-off-by: David Hildenbrand <>

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.

With the comment Vlastimil suggested:

Reviewed-by: Oscar Salvador <>

Oscar Salvador

 \ /
  Last update: 2020-09-25 15:35    [W:0.084 / U:9.484 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site