Re: [RFC 0/4] Transparent on-demand struct page initialization embedded in the buddy allocator

Robin Holt
2013-07-17T09:30:54Z

On Wed, Jul 17, 2013 at 01:17:44PM +0800, Sam Ben wrote:
> On 07/12/2013 10:03 AM, Robin Holt wrote:
> >We have been working on this since we returned from shutdown and have
> >something to discuss now. We restricted ourselves to 2MiB initialization
> >to keep the patch set a little smaller and more clear.
> >
> >First, I think I want to propose getting rid of the page flag. If I knew
> >of a concrete way to determine that the page has not been initialized,
> >this patch series would look different. If there is no definitive
> >way to determine that the struct page has been initialized aside from
> >checking the entire page struct is zero, then I think I would suggest
> >we change the page flag to indicate the page has been initialized.
> >
> >The heart of the problem as I see it comes from expand(). We nearly
> >always see a first reference to a struct page which is in the middle
> >of the 2MiB region. Due to that access, the unlikely() check that was
> >originally proposed really ends up referencing a different page entirely.
> >We actually did not introduce an unlikely and refactor the patches to
> >make that unlikely inside a static inline function. Also, given the
> >strong warning at the head of expand(), we did not feel experienced
> >enough to refactor it to make things always reference the 2MiB page
> >first.
> >
> >With this patch, we did boot a 16TiB machine. Without the patches,
> >the v3.10 kernel with the same configuration took 407 seconds for
> >free_all_bootmem. With the patches and operating on 2MiB pages instead
> >of 1GiB, it took 26 seconds so performance was improved. I have no feel
> >for how the 1GiB chunk size will perform.
>
> How to test how much time spend on free_all_bootmem?

We had put a pr_emerg at the beginning and end of free_all_bootmem and
then used a modified version of script which record the time in uSecs
at the beginning of each line of output.

Robin

>
> >
> >I am on vacation for the next three days so I am sorry in advance for
> >my infrequent or non-existant responses.
> >
> >
> >Signed-off-by: Robin Holt <holt@sgi.com>
> >Signed-off-by: Nate Zimmer <nzimmer@sgi.com>
> >To: "H. Peter Anvin" <hpa@zytor.com>
> >To: Ingo Molnar <mingo@kernel.org>
> >Cc: Linux Kernel <linux-kernel@vger.kernel.org>
> >Cc: Linux MM <linux-mm@kvack.org>
> >Cc: Rob Landley <rob@landley.net>
> >Cc: Mike Travis <travis@sgi.com>
> >Cc: Daniel J Blueman <daniel@numascale-asia.com>
> >Cc: Andrew Morton <akpm@linux-foundation.org>
> >Cc: Greg KH <gregkh@linuxfoundation.org>
> >Cc: Yinghai Lu <yinghai@kernel.org>
> >Cc: Mel Gorman <mgorman@suse.de>
> >--
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