On 2/15/22 15:51, Mel Gorman wrote:
> free_pcppages_bulk() frees pages in a round-robin fashion. Originally,
> this was dealing only with migratetypes but storing high-order pages
> means that there can be many more empty lists that are uselessly
> checked. Track the minimum and maximum active pindex to reduce the
> search space.
>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> ---
> mm/page_alloc.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 08de32cfd9bb..c5110fdeb115 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1450,6 +1450,8 @@ static void free_pcppages_bulk(struct zone *zone, int count,
> struct per_cpu_pages *pcp)
> {
> int pindex = 0;
> + int min_pindex = 0;
> + int max_pindex = NR_PCP_LISTS - 1;
> int batch_free = 0;
> int nr_freed = 0;
> unsigned int order;
> @@ -1478,10 +1480,17 @@ static void free_pcppages_bulk(struct zone *zone, int count,
> if (++pindex == NR_PCP_LISTS)
Hmm, so in the very first iteration at this point pindex is already 1. This
looks odd even before the patch, as order 0 MIGRATE_UNMOVABLE list is only
processed after all the higher orders?
> pindex = 0;
Also shouldn't this wrap-around check also use min_index/max_index instead
of NR_PCP_LISTS and 0?
> list = &pcp->lists[pindex];
> - } while (list_empty(list));
> + if (!list_empty(list))
> + break;
> +
> + if (pindex == max_pindex)
> + max_pindex--;
> + if (pindex == min_pindex)
So with pindex 1 and min_pindex == 0 this will not trigger until
(eventually) the first pindex wrap around, which seems suboptimal. But I can
see the later patches change things substantially anyway so it may be moot...
> + min_pindex++;
> + } while (1);
>
> /* This is the only non-empty list. Free them all. */
> - if (batch_free == NR_PCP_LISTS)
> + if (batch_free >= max_pindex - min_pindex)
> batch_free = count;
>
> order = pindex_to_order(pindex);
