linux-kernel - Re: [PATCH 1/4] mm, page_owner: make init_pages_in

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Message-ID: <20170724123843.GH25221@dhcp22.suse.cz>
Date:   Mon, 24 Jul 2017 14:38:43 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Yang Shi <yang.shi@...aro.org>,
        Laura Abbott <labbott@...hat.com>,
        Vinayak Menon <vinmenon@...eaurora.org>,
        zhong jiang <zhongjiang@...wei.com>
Subject: Re: [PATCH 1/4] mm, page_owner: make init_pages_in_zone() faster

On Thu 20-07-17 15:40:26, Vlastimil Babka wrote:
> In init_pages_in_zone() we currently use the generic set_page_owner() function
> to initialize page_owner info for early allocated pages. This means we
> needlessly do lookup_page_ext() twice for each page, and more importantly
> save_stack(), which has to unwind the stack and find the corresponding stack
> depot handle. Because the stack is always the same for the initialization,
> unwind it once in init_pages_in_zone() and reuse the handle. Also avoid the
> repeated lookup_page_ext().

Yes this looks like an improvement but I have to admit that I do not
really get why we even do save_stack at all here. Those pages might
got allocated from anywhere so we could very well provide a statically
allocated "fake" stack trace, no?

Memory allocated for the stackdepot storage can be tracked inside
depot_alloc_stack as well I guess (again with a statically preallocated
storage).
 
> This can significantly reduce boot times with page_owner=on on large machines,
> especially for kernels built without frame pointer, where the stack unwinding
> is noticeably slower.

Some numbders would be really nice here

> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  mm/page_owner.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 401feb070335..5aa21ca237d9 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -183,6 +183,20 @@ noinline void __set_page_owner(struct page *page, unsigned int order,
>  	__set_bit(PAGE_EXT_OWNER, &page_ext->flags);
>  }
>  
> +static void __set_page_owner_init(struct page_ext *page_ext,
> +					depot_stack_handle_t handle)
> +{
> +	struct page_owner *page_owner;
> +
> +	page_owner = get_page_owner(page_ext);
> +	page_owner->handle = handle;
> +	page_owner->order = 0;
> +	page_owner->gfp_mask = 0;
> +	page_owner->last_migrate_reason = -1;
> +
> +	__set_bit(PAGE_EXT_OWNER, &page_ext->flags);
> +}

Do we need to duplicated a part of __set_page_owner? Can we pull out
both owner and handle out __set_page_owner?
-- 
Michal Hocko
SUSE Labs