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Date: Fri, 9 Feb 2024 21:49:34 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Zi Yan <ziy@...dia.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
"Huang, Ying" <ying.huang@...el.com>, Ryan Roberts <ryan.roberts@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
David Hildenbrand <david@...hat.com>, "Yin, Fengwei"
<fengwei.yin@...el.com>, Yu Zhao <yuzhao@...gle.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Johannes Weiner <hannes@...xchg.org>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
Kemeng Shi <shikemeng@...weicloud.com>,
Mel Gorman <mgorman@...hsingularity.net>, Rohan Puri
<rohan.puri15@...il.com>, Mcgrof Chamberlain <mcgrof@...nel.org>,
Adam Manzanares <a.manzanares@...sung.com>,
"Vishal Moola (Oracle)" <vishal.moola@...il.com>
Subject: Re: [PATCH v3 3/3] mm/compaction: optimize >0 order folio compaction
with free page split.
On 2/9/24 20:57, Zi Yan wrote:
> On 9 Feb 2024, at 13:43, Vlastimil Babka wrote:
>
>> On 2/2/24 17:15, Zi Yan wrote:
>>> From: Zi Yan <ziy@...dia.com>
>>>
>>> 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@...dia.com>
>>> ---
>>> 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?
Almost/
> if (list_empty(&cc->freepages[order].pages)) {
You don't need to do that under that if ().
> int start_order;
>
> for (start_order = order + 1; start_order < NR_PAGE_ORDERS;
Just do start_order = order; ... (not order + 1).
The rest should just work.
> 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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