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Date: Mon, 15 Mar 2021 12:03:06 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Oscar Salvador <osalvador@...e.de>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>,
Michal Hocko <mhocko@...nel.org>,
Muchun Song <songmuchun@...edance.com>,
Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/4] mm,compaction: Let
isolate_migratepages_{range,block} return error codes
On 3/10/21 4:08 PM, Oscar Salvador wrote:
> Currently, isolate_migratepages_{range,block} and their callers use
> a pfn == 0 vs pfn != 0 scheme to let the caller know whether there was
> any error during isolation.
> This does not work as soon as we need to start reporting different error
> codes and make sure we pass them down the chain, so they are properly
> interpreted by functions like e.g: alloc_contig_range.
>
> Let us rework isolate_migratepages_{range,block} so we can report error
> codes.
> Since isolate_migratepages_block will stop returning the next pfn to be
> scanned, we reuse the cc->migrate_pfn field to keep track of that.
>
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
> ---
> mm/compaction.c | 48 ++++++++++++++++++++++++------------------------
> mm/internal.h | 2 +-
> mm/page_alloc.c | 7 +++----
> 3 files changed, 28 insertions(+), 29 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index e04f4476e68e..5769753a8f60 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -787,15 +787,16 @@ static bool too_many_isolated(pg_data_t *pgdat)
> *
> * Isolate all pages that can be migrated from the range specified by
> * [low_pfn, end_pfn). The range is expected to be within same pageblock.
> - * Returns zero if there is a fatal signal pending, otherwise PFN of the
> - * first page that was not scanned (which may be both less, equal to or more
> - * than end_pfn).
> + * Returns -EINTR in case we need to abort when we have too many isolated pages
> + * due to e.g: signal pending, async mode or having still pages to migrate, or 0.
> + * cc->migrate_pfn will contain the next pfn to scan (which may be both less,
> + * equal to or more that end_pfn).
> *
> * The pages are isolated on cc->migratepages list (not required to be empty),
> * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
> * is neither read nor updated.
> */
> -static unsigned long
> +static int
> isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> unsigned long end_pfn, isolate_mode_t isolate_mode)
> {
> @@ -810,6 +811,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> unsigned long next_skip_pfn = 0;
> bool skip_updated = false;
>
> + cc->migrate_pfn = low_pfn;
> +
> /*
> * Ensure that there are not too many pages isolated from the LRU
> * list by either parallel reclaimers or compaction. If there are,
> @@ -818,16 +821,16 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> while (unlikely(too_many_isolated(pgdat))) {
> /* stop isolation if there are still pages not migrated */
> if (cc->nr_migratepages)
> - return 0;
> + return -EINTR;
>
> /* async migration should just abort */
> if (cc->mode == MIGRATE_ASYNC)
> - return 0;
> + return -EINTR;
>
> congestion_wait(BLK_RW_ASYNC, HZ/10);
>
> if (fatal_signal_pending(current))
> - return 0;
> + return -EINTR;
> }
>
> cond_resched();
> @@ -1130,7 +1133,9 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> if (nr_isolated)
> count_compact_events(COMPACTISOLATED, nr_isolated);
>
> - return low_pfn;
> + cc->migrate_pfn = low_pfn;
> +
> + return 0;
> }
>
> /**
> @@ -1139,15 +1144,15 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> * @start_pfn: The first PFN to start isolating.
> * @end_pfn: The one-past-last PFN.
> *
> - * Returns zero if isolation fails fatally due to e.g. pending signal.
> - * Otherwise, function returns one-past-the-last PFN of isolated page
> - * (which may be greater than end_pfn if end fell in a middle of a THP page).
> + * Returns -EINTR in case isolation fails fatally due to e.g. pending signal,
> + * or 0.
> */
> -unsigned long
> +int
> isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
> unsigned long end_pfn)
> {
> unsigned long pfn, block_start_pfn, block_end_pfn;
> + int ret = 0;
>
> /* Scan block by block. First and last block may be incomplete */
> pfn = start_pfn;
> @@ -1166,17 +1171,17 @@ isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
> block_end_pfn, cc->zone))
> continue;
>
> - pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
> - ISOLATE_UNEVICTABLE);
> + ret = isolate_migratepages_block(cc, pfn, block_end_pfn,
> + ISOLATE_UNEVICTABLE);
>
> - if (!pfn)
> + if (ret)
> break;
>
> if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX)
> break;
> }
>
> - return pfn;
> + return ret;
> }
>
> #endif /* CONFIG_COMPACTION || CONFIG_CMA */
> @@ -1847,7 +1852,7 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
> */
> for (; block_end_pfn <= cc->free_pfn;
> fast_find_block = false,
> - low_pfn = block_end_pfn,
> + cc->migrate_pfn = low_pfn = block_end_pfn,
> block_start_pfn = block_end_pfn,
> block_end_pfn += pageblock_nr_pages) {
>
> @@ -1889,10 +1894,8 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
> }
>
> /* Perform the isolation */
> - low_pfn = isolate_migratepages_block(cc, low_pfn,
> - block_end_pfn, isolate_mode);
> -
> - if (!low_pfn)
> + if (isolate_migratepages_block(cc, low_pfn, block_end_pfn,
> + isolate_mode))
> return ISOLATE_ABORT;
>
> /*
> @@ -1903,9 +1906,6 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
> break;
> }
>
> - /* Record where migration scanner will be restarted. */
> - cc->migrate_pfn = low_pfn;
> -
> return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
> }
>
> diff --git a/mm/internal.h b/mm/internal.h
> index 9902648f2206..e670abb1154c 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -261,7 +261,7 @@ struct capture_control {
> unsigned long
> isolate_freepages_range(struct compact_control *cc,
> unsigned long start_pfn, unsigned long end_pfn);
> -unsigned long
> +int
> isolate_migratepages_range(struct compact_control *cc,
> unsigned long low_pfn, unsigned long end_pfn);
> int find_suitable_fallback(struct free_area *area, unsigned int order,
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 94467f1b85ff..2184e3ef4116 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8477,11 +8477,10 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
>
> if (list_empty(&cc->migratepages)) {
> cc->nr_migratepages = 0;
> - pfn = isolate_migratepages_range(cc, pfn, end);
> - if (!pfn) {
> - ret = -EINTR;
> + ret = isolate_migratepages_range(cc, pfn, end);
> + if (ret)
> break;
> - }
> + pfn = cc->migrate_pfn;
> tries = 0;
> } else if (++tries == 5) {
> ret = -EBUSY;
>
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