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

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Date:   Fri, 26 May 2017 08:56:23 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     "Huang\, Ying" <ying.huang@...el.com>,
        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

Ming Lei <ming.lei@...hat.com> writes:

> 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 for your information!  I will rebase my patchset on that after
they are merged.  From now on, this patch and the next one [07/13] is
only a temporary workaround for testing.

Best Regards,
Huang, Ying

> Thanks,
> Ming