On 9/11/23 21:41, Johannes Weiner wrote:
> When a block is partially outside the zone of the cursor page, the
> function cuts the range to the pivot page instead of the zone
> start. This can leave large parts of the block behind, which
> encourages incompatible page mixing down the line (ask for one type,
> get another), and thus long-term fragmentation.
>
> This triggers reliably on the first block in the DMA zone, whose
> start_pfn is 1. The block is stolen, but everything before the pivot
> page (which was often hundreds of pages) is left on the old list.
>
> Signed-off-by: Johannes Weiner <[email protected]>
Reviewed-by: Vlastimil Babka <[email protected]>
Note below:
> ---
> mm/page_alloc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index f6f658c3d394..5bbe5f3be5ad 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1652,7 +1652,7 @@ int move_freepages_block(struct zone *zone, struct page *page,
>
> /* Do not cross zone boundaries */
> if (!zone_spans_pfn(zone, start_pfn))
> - start_pfn = pfn;
> + start_pfn = zone->zone_start_pfn;
> if (!zone_spans_pfn(zone, end_pfn))
> return 0;
Culdn't we also adjust end_pfn to zone_end_pfn() so we don't just ignore the
last half-pageblock for no good reason? (or am I missing any?)
Also would stop treating end_pfn as inclusive here and in move_freepages(),
it's rather uncommon.
>
On Wed, Sep 13, 2023 at 04:40:48PM +0200, Vlastimil Babka wrote:
> On 9/11/23 21:41, Johannes Weiner wrote:
> > When a block is partially outside the zone of the cursor page, the
> > function cuts the range to the pivot page instead of the zone
> > start. This can leave large parts of the block behind, which
> > encourages incompatible page mixing down the line (ask for one type,
> > get another), and thus long-term fragmentation.
> >
> > This triggers reliably on the first block in the DMA zone, whose
> > start_pfn is 1. The block is stolen, but everything before the pivot
> > page (which was often hundreds of pages) is left on the old list.
> >
> > Signed-off-by: Johannes Weiner <[email protected]>
>
> Reviewed-by: Vlastimil Babka <[email protected]>
Thanks!
> > @@ -1652,7 +1652,7 @@ int move_freepages_block(struct zone *zone, struct page *page,
> >
> > /* Do not cross zone boundaries */
> > if (!zone_spans_pfn(zone, start_pfn))
> > - start_pfn = pfn;
> > + start_pfn = zone->zone_start_pfn;
> > if (!zone_spans_pfn(zone, end_pfn))
> > return 0;
>
> Culdn't we also adjust end_pfn to zone_end_pfn() so we don't just ignore the
> last half-pageblock for no good reason? (or am I missing any?)
> Also would stop treating end_pfn as inclusive here and in move_freepages(),
> it's rather uncommon.
You raise a good point here and in the reply to 5/6. Let me reply to
the other email.