On 08/16/2017 01:39 AM, David Rientjes wrote:
> It is pointless to migrate hugetlb memory as part of memory compaction if
> the hugetlb size is equal to the pageblock order. No defragmentation is
> occurring in this condition.
>
> It is also pointless to for the freeing scanner to scan a pageblock where
> a hugetlb page is pinned. Unconditionally skip these pageblocks, and do
> so peristently so that they are not rescanned until it is observed that
> these hugepages are no longer pinned.
>
> It would also be possible to do this by involving the hugetlb subsystem
> in marking pageblocks to no longer be skipped when they hugetlb pages are
> freed. This is a simple solution that doesn't involve any additional
> subsystems in pageblock skip manipulation.
>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> mm/compaction.c | 48 +++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 37 insertions(+), 11 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -217,6 +217,20 @@ static void reset_cached_positions(struct zone *zone)
> pageblock_start_pfn(zone_end_pfn(zone) - 1);
> }
>
> +/*
> + * Hugetlbfs pages should consistenly be skipped until updated by the hugetlb
> + * subsystem. It is always pointless to compact pages of pageblock_order and
> + * the free scanner can reconsider when no longer huge.
> + */
> +static bool pageblock_skip_persistent(struct page *page, unsigned int order)
> +{
> + if (!PageHuge(page))
> + return false;
> + if (order != pageblock_order)
> + return false;
> + return true;
Why just HugeTLBfs? There's also no point in migrating/finding free
pages in THPs. Actually, any compound page of pageblock order?
> +}
> +
> /*
> * This function is called to clear all cached information on pageblocks that
> * should be skipped for page isolation when the migrate and free page scanner
> @@ -241,6 +255,8 @@ static void __reset_isolation_suitable(struct zone *zone)
> continue;
> if (zone != page_zone(page))
> continue;
> + if (pageblock_skip_persistent(page, compound_order(page)))
> + continue;
I like the idea of how persistency is achieved by rechecking in the reset.
>
> clear_pageblock_skip(page);
> }
> @@ -448,13 +464,15 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
> * and the only danger is skipping too much.
> */
> if (PageCompound(page)) {
> - unsigned int comp_order = compound_order(page);
> -
> - if (likely(comp_order < MAX_ORDER)) {
> - blockpfn += (1UL << comp_order) - 1;
> - cursor += (1UL << comp_order) - 1;
> + const unsigned int order = compound_order(page);
> +
> + if (pageblock_skip_persistent(page, order)) {
> + set_pageblock_skip(page);
> + blockpfn = end_pfn;
> + } else if (likely(order < MAX_ORDER)) {
> + blockpfn += (1UL << order) - 1;
> + cursor += (1UL << order) - 1;
> }
Is this new code (and below) really necessary? The existing code should
already lead to skip bit being set via update_pageblock_skip()?
Thanks,
Vlastimil
> -
> goto isolate_fail;
> }
>
> @@ -771,11 +789,13 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> * danger is skipping too much.
> */
> if (PageCompound(page)) {
> - unsigned int comp_order = compound_order(page);
> -
> - if (likely(comp_order < MAX_ORDER))
> - low_pfn += (1UL << comp_order) - 1;
> + const unsigned int order = compound_order(page);
>
> + if (pageblock_skip_persistent(page, order)) {
> + set_pageblock_skip(page);
> + low_pfn = end_pfn;
> + } else if (likely(order < MAX_ORDER))
> + low_pfn += (1UL << order) - 1;
> goto isolate_fail;
> }
>
> @@ -837,7 +857,13 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> * is safe to read and it's 0 for tail pages.
> */
> if (unlikely(PageCompound(page))) {
> - low_pfn += (1UL << compound_order(page)) - 1;
> + const unsigned int order = compound_order(page);
> +
> + if (pageblock_skip_persistent(page, order)) {
> + set_pageblock_skip(page);
> + low_pfn = end_pfn;
> + } else
> + low_pfn += (1UL << order) - 1;
> goto isolate_fail;
> }
> }
>
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