From: Matthew Wilcox <willy@infradead.org>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Dave Hansen <dave.hansen@intel.com>,
Hugh Dickins <hughd@google.com>, Shaohua Li <shli@kernel.org>,
Minchan Kim <minchan@kernel.org>, Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH -mm -v2] mm, swap: Use kvzalloc to allocate some swap data structure
Date: Thu, 6 Apr 2017 06:40:24 -0700 [thread overview]
Message-ID: <20170406134024.GD31725@bombadil.infradead.org> (raw)
In-Reply-To: <20170405071058.25223-1-ying.huang@intel.com>
On Wed, Apr 05, 2017 at 03:10:58PM +0800, Huang, Ying wrote:
> In general, kmalloc() will have less memory fragmentation than
> vmalloc(). From Dave Hansen: For example, we have a two-page data
> structure. vmalloc() takes two effectively random order-0 pages,
> probably from two different 2M pages and pins them. That "kills" two
> 2M pages. kmalloc(), allocating two *contiguous* pages, is very
> unlikely to cross a 2M boundary (it theoretically could). That means
> it will only "kill" the possibility of a single 2M page. More 2M
> pages == less fragmentation.
Wait, what? How does kmalloc() manage to allocate two pages that cross
a 2MB boundary? AFAIK if you ask kmalloc to allocate N pages, it asks
the page allocator for an order-log(N) page allocation. Being a buddy
allocator, that comes back with an aligned set of pages. There's no
way it can get the last page from a 2MB region and the first page from
the next 2MB region.
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next prev parent reply other threads:[~2017-04-06 13:40 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-05 7:10 [PATCH -mm -v2] mm, swap: Use kvzalloc to allocate some swap data structure Huang, Ying
2017-04-06 13:40 ` Matthew Wilcox [this message]
2017-04-07 1:24 ` Huang, Ying
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