linux-kernel - Re: [PATCH -mm 06/13] block: Increase BIO_MAX_PAGES to PMD size if THP

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Date:   Thu, 25 May 2017 16:42:44 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        Minchan Kim <minchan@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Ming Lei <tom.leiming@...il.com>, Shaohua Li <shli@...com>,
        linux-block@...r.kernel.org
Subject: Re: [PATCH -mm 06/13] block: Increase BIO_MAX_PAGES to PMD size if
 THP_SWAP enabled

On Thu, May 25, 2017 at 02:46:28PM +0800, Huang, Ying wrote:
> From: Huang Ying <ying.huang@...el.com>
> 
> In this patch, BIO_MAX_PAGES is changed from 256 to HPAGE_PMD_NR if
> CONFIG_THP_SWAP is enabled and HPAGE_PMD_NR > 256.  This is to support
> THP (Transparent Huge Page) swap optimization.  Where the THP will be
> write to disk as a whole instead of HPAGE_PMD_NR normal pages to batch
> the various operations during swap.  And the page is likely to be
> written to disk to free memory when system memory goes really low, the
> memory pool need to be used to avoid deadlock.
> 
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Ming Lei <tom.leiming@...il.com>
> Cc: Shaohua Li <shli@...com>
> Cc: linux-block@...r.kernel.org
> ---
>  include/linux/bio.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index d1b04b0e99cf..314796486507 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -38,7 +38,15 @@
>  #define BIO_BUG_ON
>  #endif
>  
> +#ifdef CONFIG_THP_SWAP
> +#if HPAGE_PMD_NR > 256
> +#define BIO_MAX_PAGES		HPAGE_PMD_NR
> +#else
>  #define BIO_MAX_PAGES		256
> +#endif
> +#else
> +#define BIO_MAX_PAGES		256
> +#endif
>  
>  #define bio_prio(bio)			(bio)->bi_ioprio
>  #define bio_set_prio(bio, prio)		((bio)->bi_ioprio = prio)

Last time we discussed we should use multipage bvec for this usage.

I will rebase the last post on v4.12-rc and kick if off again since
the raid cleanup is just done on v4.11.

	http://marc.info/?t=148453679000002&r=1&w=2

Thanks,
Ming