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From: Vlastimil Babka <vbabka@suse.cz>
To: David Hildenbrand <david@redhat.com>, linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, linux-hyperv@vger.kernel.org,
	xen-devel@lists.xenproject.org, linux-acpi@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Matthew Wilcox <willy@infradead.org>,
	Alexander Duyck <alexander.h.duyck@linux.intel.com>,
	Oscar Salvador <osalvador@suse.de>,
	Wei Yang <richard.weiyang@linux.alibaba.com>,
	Pankaj Gupta <pankaj.gupta.linux@gmail.com>,
	Michal Hocko <mhocko@suse.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Michal Hocko <mhocko@kernel.org>,
	Dave Hansen <dave.hansen@intel.com>,
	Mike Rapoport <rppt@kernel.org>,
	Scott Cheloha <cheloha@linux.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH v2 2/5] mm/page_alloc: place pages to tail in __putback_isolated_page()
Date: Tue, 20 Oct 2020 19:18:00 +0200	[thread overview]
Message-ID: <ddeba755-eed5-d412-ffa0-4d1a6a4bc297@suse.cz> (raw)
In-Reply-To: <20201005121534.15649-3-david@redhat.com>

On 10/5/20 2:15 PM, David Hildenbrand wrote:
> __putback_isolated_page() already documents that pages will be placed to
> the tail of the freelist - this is, however, not the case for
> "order >= MAX_ORDER - 2" (see buddy_merge_likely()) - which should be
> the case for all existing users.
> 
> This change affects two users:
> - free page reporting
> - page isolation, when undoing the isolation (including memory onlining).
> 
> This behavior is desireable for pages that haven't really been touched
> lately, so exactly the two users that don't actually read/write page
> content, but rather move untouched pages.
> 
> The new behavior is especially desirable for memory onlining, where we
> allow allocation of newly onlined pages via undo_isolate_page_range()
> in online_pages(). Right now, we always place them to the head of the
> freelist, resulting in undesireable behavior: Assume we add
> individual memory chunks via add_memory() and online them right away to
> the NORMAL zone. We create a dependency chain of unmovable allocations
> e.g., via the memmap. The memmap of the next chunk will be placed onto
> previous chunks - if the last block cannot get offlined+removed, all
> dependent ones cannot get offlined+removed. While this can already be
> observed with individual DIMMs, it's more of an issue for virtio-mem
> (and I suspect also ppc DLPAR).
> 
> Document that this should only be used for optimizations, and no code
> should rely on this behavior for correction (if the order of the
> freelists ever changes).
> 
> We won't care about page shuffling: memory onlining already properly
> shuffles after onlining. free page reporting doesn't care about
> physically contiguous ranges, and there are already cases where page
> isolation will simply move (physically close) free pages to (currently)
> the head of the freelists via move_freepages_block() instead of
> shuffling. If this becomes ever relevant, we should shuffle the whole
> zone when undoing isolation of larger ranges, and after
> free_contig_range().
> 
> Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
> Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Acked-by: Michal Hocko <mhocko@suse.com>

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>


  reply	other threads:[~2020-10-20 17:18 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-05 12:15 [PATCH v2 0/5] mm: place pages to the freelist tail when onlining and undoing isolation David Hildenbrand
2020-10-05 12:15 ` [PATCH v2 1/5] mm/page_alloc: convert "report" flag of __free_one_page() to a proper flag David Hildenbrand
2020-10-05 12:15 ` [PATCH v2 2/5] mm/page_alloc: place pages to tail in __putback_isolated_page() David Hildenbrand
2020-10-20 17:18   ` Vlastimil Babka [this message]
2020-10-05 12:15 ` [PATCH v2 3/5] mm/page_alloc: move pages to tail in move_to_free_list() David Hildenbrand
2020-10-06 12:12   ` Michal Hocko
2020-10-20 17:20   ` Vlastimil Babka
2020-10-05 12:15 ` [PATCH v2 4/5] mm/page_alloc: place pages to tail in __free_pages_core() David Hildenbrand
2021-09-07 22:40   ` Sean Anderson
2021-09-08  6:21     ` David Hildenbrand
2021-09-10 23:06       ` Sean Anderson
2020-10-05 12:15 ` [PATCH v2 5/5] mm/memory_hotplug: update comment regarding zone shuffling David Hildenbrand
2020-10-20 17:21   ` Vlastimil Babka
2020-10-21 10:58   ` Pankaj Gupta

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