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From: David Hildenbrand <david@redhat.com>
To: Ben Widawsky <ben.widawsky@intel.com>, linux-mm <linux-mm@kvack.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	"Scargall, Steve" <steve.scargall@intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Vishal Verma <vishal.l.verma@intel.com>
Subject: Re: [PATCH] mm: Fix false softlockup during pfn range removal
Date: Tue, 23 Jun 2020 09:18:03 +0200	[thread overview]
Message-ID: <2ae36a39-79b5-7891-fc39-65e18f61e4ed@redhat.com> (raw)
In-Reply-To: <20200619231213.1160351-1-ben.widawsky@intel.com>

On 20.06.20 01:12, Ben Widawsky wrote:
> When working with very large nodes, poisoning the struct pages (for
> which there will be very many) can take a very long time. If the system
> is using voluntary preemptions, the software watchdog will not be able
> to detect forward progress. This patch addresses this issue by offering
> to give up time like __remove_pages() does.  This behavior was
> introduced in v5.6 with:
> commit d33695b16a9f ("mm/memory_hotplug: poison memmap in remove_pfn_range_from_zone()")
> 
> Alternately, init_page_poison could do this cond_resched(), but it seems
> to me that the caller of init_page_poison() is what actually knows
> whether or not it should relax its own priority.
> 
> Based on Dan's notes, I think this is perfectly safe:
> commit f931ab479dd2 ("mm: fix devm_memremap_pages crash, use mem_hotplug_{begin, done}")
> 
> Aside from fixing the lockup, it is also a friendlier thing to do on
> lower core systems that might wipe out large chunks of hotplug memory
> (probably not a very common case).

BTW, I think this is even a fix for !VMEMMAP. page_init_poison() will
just do a memset. This is only guaranteed to work on section basis
correctly without SPARSE_VMEMMAP.

Thanks!

-- 
Thanks,

David / dhildenb



      parent reply	other threads:[~2020-06-23  7:18 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-19 23:12 [PATCH] mm: Fix false softlockup during pfn range removal Ben Widawsky
2020-06-22  7:16 ` David Hildenbrand
2020-06-22 16:25   ` Ben Widawsky
2020-06-22 16:29     ` David Hildenbrand
2020-06-23  7:18 ` David Hildenbrand [this message]

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