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Message-ID: <c27bb73a-9dde-94c1-f2fe-92a71ff268b2@huawei.com>
Date: Sun, 29 Jan 2023 09:47:43 +0800
From: Chen Wandun <chenwandun@...wei.com>
To: "Huang, Ying" <ying.huang@...el.com>
CC: Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
<linux-kernel@...r.kernel.org>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
Zi Yan <ziy@...dia.com>, Yang Shi <shy828301@...il.com>,
Oscar Salvador <osalvador@...e.de>,
Matthew Wilcox <willy@...radead.org>,
Bharata B Rao <bharata@....com>,
Alistair Popple <apopple@...dia.com>,
haoxin <xhao@...ux.alibaba.com>, Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH -v3 2/9] migrate_pages: separate hugetlb folios migration
在 2023/1/29 8:36, Huang, Ying 写道:
> Chen Wandun <chenwandun@...wei.com> writes:
>
>> On 2023/1/16 14:30, Huang Ying wrote:
>>> This is a preparation patch to batch the folio unmapping and moving
>>> for the non-hugetlb folios. Based on that we can batch the TLB
>>> shootdown during the folio migration and make it possible to use some
>>> hardware accelerator for the folio copying.
>>>
>>> In this patch the hugetlb folios and non-hugetlb folios migration is
>>> separated in migrate_pages() to make it easy to change the non-hugetlb
>>> folios migration implementation.
>>>
>>> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
>>> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>>> Cc: Zi Yan <ziy@...dia.com>
>>> Cc: Yang Shi <shy828301@...il.com>
>>> Cc: Oscar Salvador <osalvador@...e.de>
>>> Cc: Matthew Wilcox <willy@...radead.org>
>>> Cc: Bharata B Rao <bharata@....com>
>>> Cc: Alistair Popple <apopple@...dia.com>
>>> Cc: haoxin <xhao@...ux.alibaba.com>
>>> Cc: Minchan Kim <minchan@...nel.org>
>>> ---
>>> mm/migrate.c | 141 +++++++++++++++++++++++++++++++++++++++++++--------
>>> 1 file changed, 119 insertions(+), 22 deletions(-)
>>>
>>> diff --git a/mm/migrate.c b/mm/migrate.c
>>> index ef388a9e4747..be7f37523463 100644
>>> --- a/mm/migrate.c
>>> +++ b/mm/migrate.c
>>> @@ -1396,6 +1396,8 @@ static inline int try_split_folio(struct folio *folio, struct list_head *split_f
>>> return rc;
>>> }
>>> +#define NR_MAX_MIGRATE_PAGES_RETRY 10
>>> +
>>> struct migrate_pages_stats {
>>> int nr_succeeded; /* Normal and large folios migrated successfully, in
>>> units of base pages */
>>> @@ -1406,6 +1408,95 @@ struct migrate_pages_stats {
>>> int nr_thp_split; /* THP split before migrating */
>>> };
>>> +/*
>>> + * Returns the number of hugetlb folios that were not migrated, or an error code
>>> + * after NR_MAX_MIGRATE_PAGES_RETRY attempts or if no hugetlb folios are movable
>>> + * any more because the list has become empty or no retryable hugetlb folios
>>> + * exist any more. It is caller's responsibility to call putback_movable_pages()
>>> + * only if ret != 0.
>>> + */
>>> +static int migrate_hugetlbs(struct list_head *from, new_page_t get_new_page,
>>> + free_page_t put_new_page, unsigned long private,
>>> + enum migrate_mode mode, int reason,
>>> + struct migrate_pages_stats *stats,
>>> + struct list_head *ret_folios)
>>> +{
>>> + int retry = 1;
>>> + int nr_failed = 0;
>>> + int nr_retry_pages = 0;
>>> + int pass = 0;
>>> + struct folio *folio, *folio2;
>>> + int rc, nr_pages;
>>> +
>>> + for (pass = 0; pass < NR_MAX_MIGRATE_PAGES_RETRY && retry; pass++) {
>>> + retry = 0;
>>> + nr_retry_pages = 0;
>>> +
>>> + list_for_each_entry_safe(folio, folio2, from, lru) {
>>> + if (!folio_test_hugetlb(folio))
>>> + continue;
>>> +
>>> + nr_pages = folio_nr_pages(folio);
>>> +
>>> + cond_resched();
>>> +
>>> + rc = unmap_and_move_huge_page(get_new_page,
>>> + put_new_page, private,
>>> + &folio->page, pass > 2, mode,
>>> + reason, ret_folios);
>>> + /*
>>> + * The rules are:
>>> + * Success: hugetlb folio will be put back
>>> + * -EAGAIN: stay on the from list
>>> + * -ENOMEM: stay on the from list
>>> + * -ENOSYS: stay on the from list
>>> + * Other errno: put on ret_folios list
>>> + */
>>> + switch(rc) {
>>> + case -ENOSYS:
>>> + /* Hugetlb migration is unsupported */
>>> + nr_failed++;
>>> + stats->nr_failed_pages += nr_pages;
>>> + list_move_tail(&folio->lru, ret_folios);
>>> + break;
>>> + case -ENOMEM:
>>> + /*
>>> + * When memory is low, don't bother to try to migrate
>>> + * other folios, just exit.
>>> + */
>>> + stats->nr_failed_pages += nr_pages + nr_retry_pages;
>>> + return -ENOMEM;
>>> + case -EAGAIN:
>>> + retry++;
>>> + nr_retry_pages += nr_pages;
>>> + break;
>>> + case MIGRATEPAGE_SUCCESS:
>>> + stats->nr_succeeded += nr_pages;
>>> + break;
>>> + default:
>>> + /*
>>> + * Permanent failure (-EBUSY, etc.):
>>> + * unlike -EAGAIN case, the failed folio is
>>> + * removed from migration folio list and not
>>> + * retried in the next outer loop.
>>> + */
>>> + nr_failed++;
>>> + stats->nr_failed_pages += nr_pages;
>>> + break;
>>> + }
>>> + }
>>> + }
>>> + /*
>>> + * nr_failed is number of hugetlb folios failed to be migrated. After
>>> + * NR_MAX_MIGRATE_PAGES_RETRY attempts, give up and count retried hugetlb
>>> + * folios as failed.
>>> + */
>>> + nr_failed += retry;
>>> + stats->nr_failed_pages += nr_retry_pages;
>>> +
>>> + return nr_failed;
>>> +}
>>> +
>>> /*
>>> * migrate_pages - migrate the folios specified in a list, to the free folios
>>> * supplied as the target for the page migration
>>> @@ -1422,10 +1513,10 @@ struct migrate_pages_stats {
>>> * @ret_succeeded: Set to the number of folios migrated successfully if
>>> * the caller passes a non-NULL pointer.
>>> *
>>> - * The function returns after 10 attempts or if no folios are movable any more
>>> - * because the list has become empty or no retryable folios exist any more.
>>> - * It is caller's responsibility to call putback_movable_pages() to return folios
>>> - * to the LRU or free list only if ret != 0.
>>> + * The function returns after NR_MAX_MIGRATE_PAGES_RETRY attempts or if no folios
>>> + * are movable any more because the list has become empty or no retryable folios
>>> + * exist any more. It is caller's responsibility to call putback_movable_pages()
>>> + * only if ret != 0.
>>> *
>>> * Returns the number of {normal folio, large folio, hugetlb} that were not
>>> * migrated, or an error code. The number of large folio splits will be
>>> @@ -1439,7 +1530,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>> int retry = 1;
>>> int large_retry = 1;
>>> int thp_retry = 1;
>>> - int nr_failed = 0;
>>> + int nr_failed;
>>> int nr_retry_pages = 0;
>>> int nr_large_failed = 0;
>>> int pass = 0;
>>> @@ -1456,38 +1547,45 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>>> trace_mm_migrate_pages_start(mode, reason);
>>> memset(&stats, 0, sizeof(stats));
>>> + rc = migrate_hugetlbs(from, get_new_page, put_new_page, private, mode, reason,
>>> + &stats, &ret_folios);
>>> + if (rc < 0)
>>> + goto out;
>> How about continue migrate small page for -ENOMEM case? maybe
>> there are still
>> free small pages.
> Sounds reasonable to me. How about do that on top of this series? Do
> you have interest to do that?
Happy to do that, thanks for you reply.
Best Regards,
Wandun
>
> Best Regards,
> Huang, Ying
>
> .
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