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Date: Thu, 14 Mar 2019 09:10:52 +0100
From: Oscar Salvador <osalvador@...e.de>
To: Qian Cai <cai@....pw>
Cc: akpm@...ux-foundation.org, mhocko@...nel.org, vbabka@...e.cz,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/hotplug: fix offline undo_isolate_page_range()
On Wed, Mar 13, 2019 at 10:31:33AM -0400, Qian Cai wrote:
> The commit f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded
> memory to zones until online") introduced move_pfn_range_to_zone() which
> calls memmap_init_zone() during onlining a memory block.
> memmap_init_zone() will reset pagetype flags and makes migrate type to
> be MOVABLE.
>
> However, in __offline_pages(), it also call undo_isolate_page_range()
> after offline_isolated_pages() to do the same thing. Due to
> the commit 2ce13640b3f4 ("mm: __first_valid_page skip over offline
> pages") changed __first_valid_page() to skip offline pages,
> undo_isolate_page_range() here just waste CPU cycles looping around the
> offlining PFN range while doing nothing, because __first_valid_page()
> will return NULL as offline_isolated_pages() has already marked all
> memory sections within the pfn range as offline via
> offline_mem_sections().
>
> Also, after calling the "useless" undo_isolate_page_range() here, it
> reaches the point of no returning by notifying MEM_OFFLINE. Those pages
> will be marked as MIGRATE_MOVABLE again once onlining. The only thing
> left to do is to decrease the number of isolated pageblocks zone
> counter which would make some paths of the page allocation slower that
> the above commit introduced. A memory block is usually at most 1GiB in
> size, so an "int" should be enough to represent the number of pageblocks
> in a block. Fix an incorrect comment along the way.
>
> Fixes: 2ce13640b3f4 ("mm: __first_valid_page skip over offline pages")
> Signed-off-by: Qian Cai <cai@....pw>
Forgot it:
Reviewed-by: Oscar Salvador <osalvador@...e.de>
> ---
>
> v2: return the nubmer of isolated pageblocks in start_isolate_page_range() per
> Oscar; take the zone lock when undoing zone->nr_isolate_pageblock per
> Michal.
>
> mm/memory_hotplug.c | 17 +++++++++++++----
> mm/page_alloc.c | 2 +-
> mm/page_isolation.c | 16 ++++++++++------
> mm/sparse.c | 2 +-
> 4 files changed, 25 insertions(+), 12 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index cd23c081924d..8ffe844766da 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1580,7 +1580,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
> {
> unsigned long pfn, nr_pages;
> long offlined_pages;
> - int ret, node;
> + int ret, node, count;
> unsigned long flags;
> unsigned long valid_start, valid_end;
> struct zone *zone;
> @@ -1606,10 +1606,11 @@ static int __ref __offline_pages(unsigned long start_pfn,
> ret = start_isolate_page_range(start_pfn, end_pfn,
> MIGRATE_MOVABLE,
> SKIP_HWPOISON | REPORT_FAILURE);
> - if (ret) {
> + if (ret < 0) {
> reason = "failure to isolate range";
> goto failed_removal;
> }
> + count = ret;
>
> arg.start_pfn = start_pfn;
> arg.nr_pages = nr_pages;
> @@ -1661,8 +1662,16 @@ static int __ref __offline_pages(unsigned long start_pfn,
> /* Ok, all of our target is isolated.
> We cannot do rollback at this point. */
> offline_isolated_pages(start_pfn, end_pfn);
> - /* reset pagetype flags and makes migrate type to be MOVABLE */
> - undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
> +
> + /*
> + * Onlining will reset pagetype flags and makes migrate type
> + * MOVABLE, so just need to decrease the number of isolated
> + * pageblocks zone counter here.
> + */
> + spin_lock_irqsave(&zone->lock, flags);
> + zone->nr_isolate_pageblock -= count;
> + spin_unlock_irqrestore(&zone->lock, flags);
> +
> /* removal success */
> adjust_managed_page_count(pfn_to_page(start_pfn), -offlined_pages);
> zone->present_pages -= offlined_pages;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 03fcf73d47da..d96ca5bc555b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8233,7 +8233,7 @@ int alloc_contig_range(unsigned long start, unsigned long end,
>
> ret = start_isolate_page_range(pfn_max_align_down(start),
> pfn_max_align_up(end), migratetype, 0);
> - if (ret)
> + if (ret < 0)
> return ret;
>
> /*
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index ce323e56b34d..bf67b63227ca 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -172,7 +172,8 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
> * future will not be allocated again.
> *
> * start_pfn/end_pfn must be aligned to pageblock_order.
> - * Return 0 on success and -EBUSY if any part of range cannot be isolated.
> + * Return the number of isolated pageblocks on success and -EBUSY if any part of
> + * range cannot be isolated.
> *
> * There is no high level synchronization mechanism that prevents two threads
> * from trying to isolate overlapping ranges. If this happens, one thread
> @@ -188,6 +189,7 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> unsigned long pfn;
> unsigned long undo_pfn;
> struct page *page;
> + int count = 0;
>
> BUG_ON(!IS_ALIGNED(start_pfn, pageblock_nr_pages));
> BUG_ON(!IS_ALIGNED(end_pfn, pageblock_nr_pages));
> @@ -196,13 +198,15 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> pfn < end_pfn;
> pfn += pageblock_nr_pages) {
> page = __first_valid_page(pfn, pageblock_nr_pages);
> - if (page &&
> - set_migratetype_isolate(page, migratetype, flags)) {
> - undo_pfn = pfn;
> - goto undo;
> + if (page) {
> + if (set_migratetype_isolate(page, migratetype, flags)) {
> + undo_pfn = pfn;
> + goto undo;
> + }
> + count++;
> }
> }
> - return 0;
> + return count;
> undo:
> for (pfn = start_pfn;
> pfn < undo_pfn;
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 69904aa6165b..56e057c432f9 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -567,7 +567,7 @@ void online_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
> }
>
> #ifdef CONFIG_MEMORY_HOTREMOVE
> -/* Mark all memory sections within the pfn range as online */
> +/* Mark all memory sections within the pfn range as offline */
> void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
> {
> unsigned long pfn;
> --
> 2.17.2 (Apple Git-113)
>
--
Oscar Salvador
SUSE L3
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