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Date: Wed, 1 Mar 2023 11:08:26 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Huang Ying <ying.huang@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Hugh Dickins <hughd@...gle.com>,
"Xu, Pengfei" <pengfei.xu@...el.com>,
Christoph Hellwig <hch@....de>,
Stefan Roesch <shr@...kernel.io>, Tejun Heo <tj@...nel.org>,
Xin Hao <xhao@...ux.alibaba.com>, Zi Yan <ziy@...dia.com>,
Yang Shi <shy828301@...il.com>,
Matthew Wilcox <willy@...radead.org>,
Mike Kravetz <mike.kravetz@...cle.com>
Subject: Re: [PATCH 3/3] migrate_pages: try migrate in batch asynchronously
firstly
On 2/24/2023 10:11 PM, Huang Ying wrote:
> When we have locked more than one folios, we cannot wait the lock or
> bit (e.g., page lock, buffer head lock, writeback bit) synchronously.
> Otherwise deadlock may be triggered. This make it hard to batch the
> synchronous migration directly.
>
> This patch re-enables batching synchronous migration via trying to
> migrate in batch asynchronously firstly. And any folios that are
> failed to be migrated asynchronously will be migrated synchronously
> one by one.
>
> Test shows that this can restore the TLB flushing batching performance
> for synchronous migration effectively.
>
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: "Xu, Pengfei" <pengfei.xu@...el.com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Stefan Roesch <shr@...kernel.io>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Xin Hao <xhao@...ux.alibaba.com>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: Yang Shi <shy828301@...il.com>
> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Mike Kravetz <mike.kravetz@...cle.com>
> ---
> mm/migrate.c | 65 ++++++++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 55 insertions(+), 10 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 91198b487e49..c17ce5ee8d92 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1843,6 +1843,51 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
> return rc;
> }
>
> +static int migrate_pages_sync(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 list_head *ret_folios,
> + struct list_head *split_folios, struct migrate_pages_stats *stats)
> +{
> + int rc, nr_failed = 0;
> + LIST_HEAD(folios);
> + struct migrate_pages_stats astats;
> +
> + memset(&astats, 0, sizeof(astats));
> + /* Try to migrate in batch with MIGRATE_ASYNC mode firstly */
> + rc = migrate_pages_batch(from, get_new_page, put_new_page, private, MIGRATE_ASYNC,
> + reason, &folios, split_folios, &astats,
> + NR_MAX_MIGRATE_PAGES_RETRY);
> + stats->nr_succeeded += astats.nr_succeeded;
> + stats->nr_thp_succeeded += astats.nr_thp_succeeded;
> + stats->nr_thp_split += astats.nr_thp_split;
> + if (rc < 0) {
> + stats->nr_failed_pages += astats.nr_failed_pages;
> + stats->nr_thp_failed += astats.nr_thp_failed;
> + list_splice_tail(&folios, ret_folios);
> + return rc;
> + }
> + stats->nr_thp_failed += astats.nr_thp_split;
> + nr_failed += astats.nr_thp_split;
> + /*
> + * Fall back to migrate all failed folios one by one synchronously. All
> + * failed folios except split THPs will be retried, so their failure
> + * isn't counted
> + */
> + list_splice_tail_init(&folios, from);
> + while (!list_empty(from)) {
> + list_move(from->next, &folios);
> + rc = migrate_pages_batch(&folios, get_new_page, put_new_page,
> + private, mode, reason, ret_folios,
> + split_folios, stats, NR_MAX_MIGRATE_PAGES_RETRY);
> + list_splice_tail_init(&folios, ret_folios);
> + if (rc < 0)
> + return rc;
> + nr_failed += rc;
> + }
> +
> + return nr_failed;
> +}
> +
> /*
> * migrate_pages - migrate the folios specified in a list, to the free folios
> * supplied as the target for the page migration
> @@ -1874,7 +1919,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> enum migrate_mode mode, int reason, unsigned int *ret_succeeded)
> {
> int rc, rc_gather;
> - int nr_pages, batch;
> + int nr_pages;
> struct folio *folio, *folio2;
> LIST_HEAD(folios);
> LIST_HEAD(ret_folios);
> @@ -1890,10 +1935,6 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> if (rc_gather < 0)
> goto out;
>
> - if (mode == MIGRATE_ASYNC)
> - batch = NR_MAX_BATCHED_MIGRATION;
> - else
> - batch = 1;
> again:
> nr_pages = 0;
> list_for_each_entry_safe(folio, folio2, from, lru) {
> @@ -1904,16 +1945,20 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> }
>
> nr_pages += folio_nr_pages(folio);
> - if (nr_pages >= batch)
> + if (nr_pages >= NR_MAX_BATCHED_MIGRATION)
> break;
> }
> - if (nr_pages >= batch)
> + if (nr_pages >= NR_MAX_BATCHED_MIGRATION)
> list_cut_before(&folios, from, &folio2->lru);
> else
> list_splice_init(from, &folios);
> - rc = migrate_pages_batch(&folios, get_new_page, put_new_page, private,
> - mode, reason, &ret_folios, &split_folios, &stats,
> - NR_MAX_MIGRATE_PAGES_RETRY);
> + if (mode == MIGRATE_ASYNC)
> + rc = migrate_pages_batch(&folios, get_new_page, put_new_page, private,
> + mode, reason, &ret_folios, &split_folios, &stats,
> + NR_MAX_MIGRATE_PAGES_RETRY);
> + else
> + rc = migrate_pages_sync(&folios, get_new_page, put_new_page, private,
> + mode, reason, &ret_folios, &split_folios, &stats);
For split folios, it seems also reasonable to use migrate_pages_sync()
instead of always using fixed MIGRATE_ASYNC mode?
> list_splice_tail_init(&folios, &ret_folios);
> if (rc < 0) {
> rc_gather = rc;
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