On 9 Feb 2024, at 13:43, Vlastimil Babka wrote:
> On 2/2/24 17:15, Zi Yan wrote:
>> From: Zi Yan <ziy@xxxxxxxxxx>
>>
>> During migration in a memory compaction, free pages are placed in an array
>> of page lists based on their order. But the desired free page order (i.e.,
>> the order of a source page) might not be always present, thus leading to
>> migration failures and premature compaction termination. Split a high
>> order free pages when source migration page has a lower order to increase
>> migration successful rate.
>>
>> Note: merging free pages when a migration fails and a lower order free
>> page is returned via compaction_free() is possible, but there is too much
>> work. Since the free pages are not buddy pages, it is hard to identify
>> these free pages using existing PFN-based page merging algorithm.
>>
>> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
>> ---
>> mm/compaction.c | 37 ++++++++++++++++++++++++++++++++++++-
>> 1 file changed, 36 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 58a4e3fb72ec..fa9993c8a389 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -1832,9 +1832,43 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
>> struct compact_control *cc = (struct compact_control *)data;
>> struct folio *dst;
>> int order = folio_order(src);
>> + bool has_isolated_pages = false;
>>
>> +again:
>> if (!cc->freepages[order].nr_pages) {
>> - isolate_freepages(cc);
>> + int i;
>> +
>> + for (i = order + 1; i < NR_PAGE_ORDERS; i++) {
>
> You could probably just start with a loop that finds the start_order (and do
> the isolate_freepages() attempt if there's none) and then handle the rest
> outside of the loop. No need to separately handle the case where you have
> the exact order available?
Like this?
if (list_empty(&cc->freepages[order].pages)) {
int start_order;
for (start_order = order + 1; start_order < NR_PAGE_ORDERS;
start_order++)
if (!list_empty(&cc->freepages[start_order].pages))
break;
/* no free pages in the list */
if (start_order == NR_PAGE_ORDERS) {
if (!has_isolated_pages) {
isolate_freepages(cc);
has_isolated_pages = true;
goto again;
} else
return NULL;
}
struct page *freepage =
list_first_entry(&cc->freepages[start_order].pages,
struct page, lru);
unsigned long size = 1 << start_order;
list_del(&freepage->lru);
while (start_order > order) {
start_order--;
size >>= 1;
list_add(&freepage[size].lru,
&cc->freepages[start_order].pages);
set_page_private(&freepage[size], start_order);
}
dst = (struct folio *)freepage;
goto done;
}
>
>> + if (cc->freepages[i].nr_pages) {
>> + struct page *freepage =
>> + list_first_entry(&cc->freepages[i].pages,
>> + struct page, lru);
>> +
>> + int start_order = i;
>> + unsigned long size = 1 << start_order;
>> +
>> + list_del(&freepage->lru);
>> + cc->freepages[i].nr_pages--;
>> +
>> + while (start_order > order) {
>
> With exact order available this while loop will just be skipped and that's
> all the difference to it?
>
>> + start_order--;
>> + size >>= 1;
>> +
>> + list_add(&freepage[size].lru,
>> + &cc->freepages[start_order].pages);
>> + cc->freepages[start_order].nr_pages++;
>> + set_page_private(&freepage[size], start_order);
>> + }
>> + dst = (struct folio *)freepage;
>> + goto done;
>> + }
>> + }
>> + if (!has_isolated_pages) {
>> + isolate_freepages(cc);
>> + has_isolated_pages = true;
>> + goto again;
>> + }
>> +
>> if (!cc->freepages[order].nr_pages)
>> return NULL;
>> }
>> @@ -1842,6 +1876,7 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
>> dst = list_first_entry(&cc->freepages[order].pages, struct folio, lru);
>> cc->freepages[order].nr_pages--;
>> list_del(&dst->lru);
>> +done:
>> post_alloc_hook(&dst->page, order, __GFP_MOVABLE);
>> if (order)
>> prep_compound_page(&dst->page, order);
--
Best Regards,
Yan, Zi
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