linux-kernel - Re: [PATCH 5/8] migrate_pages: batch _unmap and

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Message-ID: <87lemjnnmh.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Wed, 04 Jan 2023 08:34:46 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Zi Yan <ziy@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, Yang Shi <shy828301@...il.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Oscar Salvador <osalvador@...e.de>,
        "Matthew Wilcox" <willy@...radead.org>,
        Bharata B Rao <bharata@....com>,
        "Alistair Popple" <apopple@...dia.com>,
        haoxin <xhao@...ux.alibaba.com>
Subject: Re: [PATCH 5/8] migrate_pages: batch _unmap and _move

Zi Yan <ziy@...dia.com> writes:

> On 26 Dec 2022, at 19:28, Huang Ying wrote:
>
>> In this patch the _unmap and _move stage of the folio migration is
>> batched.  That for, previously, it is,
>>
>>   for each folio
>>     _unmap()
>>     _move()
>>
>> Now, it is,
>>
>>   for each folio
>>     _unmap()
>>   for each folio
>>     _move()
>
> Also worth adding some notes here, we need extra code to undo the _unmap()
> if _move() fails. Andrew has asked for comments on *_undo_src/dst(),
> but I think it would be better to provide a high level new workflow,
> in the form of pseudo code, in git log and the comment for migrate_pages().
> The extra cleanup code for a failed _move() with a previously successful
> _unmap() might not be obvious to everyone.

Here, I removed the detailed error processing to make it easier to
understand the basic flow changing.  So, I would rather to keep the
pseudo code here as simple as possible and keep the detailed flow in the
diff below.

Best Regards,
Huang, Ying

>>
>> Based on this, we can batch the TLB flushing and use some hardware
>> accelerator to copy folios between batched _unmap and batched _move
>> stages.
>>

[snip]