linux-kernel - Re: [PATCH v4 3/3] mm/compaction: optimize >0 order folio compaction with free page split.

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Date: Mon, 12 Feb 2024 13:29:38 -0500
From: Zi Yan <ziy@...dia.com>
To: Yu Zhao <yuzhao@...gle.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>, Vlastimil Babka <vbabka@...e.cz>,
 "\"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 v4 3/3] mm/compaction: optimize >0 order folio compaction
 with free page split.

On 12 Feb 2024, at 13:27, Yu Zhao wrote:

> On Mon, Feb 12, 2024 at 9:35 AM Zi Yan <zi.yan@...t.com> 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>
>> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> Tested-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> Cc: Adam Manzanares <a.manzanares@...sung.com>
>> Cc: David Hildenbrand <david@...hat.com>
>> Cc: Huang Ying <ying.huang@...el.com>
>> Cc: Johannes Weiner <hannes@...xchg.org>
>> Cc: Kemeng Shi <shikemeng@...weicloud.com>
>> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>> Cc: Luis Chamberlain <mcgrof@...nel.org>
>> Cc: Matthew Wilcox (Oracle) <willy@...radead.org>
>> Cc: Mel Gorman <mgorman@...hsingularity.net>
>> Cc: Ryan Roberts <ryan.roberts@....com>
>> Cc: Vishal Moola (Oracle) <vishal.moola@...il.com>
>> Cc: Vlastimil Babka <vbabka@...e.cz>
>> Cc: Yin Fengwei <fengwei.yin@...el.com>
>> Cc: Yu Zhao <yuzhao@...gle.com>
>> ---
>>  mm/compaction.c | 36 +++++++++++++++++++++++++++++++-----
>>  1 file changed, 31 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index d0a05a621b67..25908e36b97c 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -1832,15 +1832,41 @@ 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;
>> +       int start_order;
>> +       struct page *freepage;
>> +       unsigned long size;
>> +
>> +again:
>> +       for (start_order = order; start_order < NR_PAGE_ORDERS; start_order++)
>> +               if (!list_empty(&cc->freepages[start_order]))
>> +                       break;
>>
>> -       if (list_empty(&cc->freepages[order])) {
>> -               isolate_freepages(cc);
>> -               if (list_empty(&cc->freepages[order]))
>> +       /* 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;
>
> Nit: remove the "else" above, or just:
>
>         if (has_isolated_pages)
>                 return NULL;
>         isolate_freepages(cc);
>         has_isolated_pages = true;
>         goto again;

Will do. Thanks.

--
Best Regards,
Yan, Zi

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