On 15 Feb 2024, at 11:07, Vlastimil Babka wrote:
> On 2/14/24 23:04, Zi Yan wrote:
>> From: Zi Yan <ziy@xxxxxxxxxx>
>>
>> Before last commit, memory compaction only migrates order-0 folios and
>> skips >0 order folios. Last commit splits all >0 order folios during
>> compaction. This commit migrates >0 order folios during compaction by
>> keeping isolated free pages at their original size without splitting them
>> into order-0 pages and using them directly during migration process.
>>
>> What is different from the prior implementation:
>> 1. All isolated free pages are kept in a NR_PAGE_ORDERS array of page
>> lists, where each page list stores free pages in the same order.
>> 2. All free pages are not post_alloc_hook() processed nor buddy pages,
>> although their orders are stored in first page's private like buddy
>> pages.
>> 3. During migration, in new page allocation time (i.e., in
>> compaction_alloc()), free pages are then processed by post_alloc_hook().
>> When migration fails and a new page is returned (i.e., in
>> compaction_free()), free pages are restored by reversing the
>> post_alloc_hook() operations using newly added
>> free_pages_prepare_fpi_none().
>>
>> Step 3 is done for a latter optimization that splitting and/or merging
>> free pages during compaction becomes easier.
>>
>> Note: without splitting free pages, compaction can end prematurely due to
>> migration will return -ENOMEM even if there is free pages. This happens
>> when no order-0 free page exist and compaction_alloc() return NULL.
>>
>> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
>> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>> Tested-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>> Tested-by: Yu Zhao <yuzhao@xxxxxxxxxx>
>
> Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Thanks.
>
> Noticed a possible simplification:
>
>> --- a/mm/internal.h
>> +++ b/mm/internal.h
>> @@ -447,6 +447,8 @@ extern void prep_compound_page(struct page *page, unsigned int order);
>>
>> extern void post_alloc_hook(struct page *page, unsigned int order,
>> gfp_t gfp_flags);
>> +extern bool free_pages_prepare_fpi_none(struct page *page, unsigned int order);
>> +
>> extern int user_min_free_kbytes;
>>
>> extern void free_unref_page(struct page *page, unsigned int order);
>> @@ -481,7 +483,7 @@ int split_free_page(struct page *free_page,
>> * completes when free_pfn <= migrate_pfn
>> */
>> struct compact_control {
>> - struct list_head freepages; /* List of free pages to migrate to */
>> + struct list_head freepages[NR_PAGE_ORDERS]; /* List of free pages to migrate to */
>> struct list_head migratepages; /* List of pages being migrated */
>> unsigned int nr_freepages; /* Number of isolated free pages */
>> unsigned int nr_migratepages; /* Number of pages to migrate */
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 7ae4b74c9e5c..e6e2ac722a82 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1179,6 +1179,12 @@ static __always_inline bool free_pages_prepare(struct page *page,
>> return true;
>> }
>>
>> +__always_inline bool free_pages_prepare_fpi_none(struct page *page,
>> + unsigned int order)
>> +{
>> + return free_pages_prepare(page, order, FPI_NONE);
>
> Seems like free_pages_prepare() currently only passes fpi_flags to
> should_skip_kasan_poison() and that ignores them. You could remove the
> parameter from both and declare and use free_pages_prepare(page, order)
> directly.
Got it. I can send a cleanup patch after this series. No, to avoid unnecessary
code churn, it is better to put a cleanup patch before this series and use
free_pages_prepare(). Will do it in v6.
>> +}
>> +
>> /*
>> * Frees a number of pages from the PCP lists
>> * Assumes all pages on list are in same zone.
--
Best Regards,
Yan, Zi
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