linux-kernel - Re: [PATCH v2 0/5] Fix the incorrect memmep defer init handling and do some cleanup

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Date:   Tue, 22 Dec 2020 17:46:58 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        gopakumarr@...are.com, rppt@...nel.org, david@...hat.com
Subject: Re: [PATCH v2 0/5] Fix the incorrect memmep defer init handling and
 do some cleanup

On Sun, 20 Dec 2020 16:27:49 +0800 Baoquan He <bhe@...hat.com> wrote:

> VMware reported the performance regression during memmap_init() invocation.
> And they bisected to commit 73a6e474cb376 ("mm: memmap_init: iterate over
> memblock regions rather that check each PFN") causing it.
> 
> https://lore.kernel.org/linux-mm/DM6PR05MB52921FF90FA01CC337DD23A1A4080@DM6PR05MB5292.namprd05.prod.outlook.com/
> 
> After investigation, it's caused by incorrect memmap init defer handling
> in memmap_init_zone() after commit 73a6e474cb376. The current
> memmap_init_zone() only handle one memory region of one zone, while
> memmap_init() iterates over all its memory regions and pass them one by
> one into memmap_init_zone() to handle.
> 
> So in this patchset, patch 1/5 fixes the bug observed by VMware. Patch
> 2~5/5 clean up codes.
> accordingly.

This series doesn't apply well to current mainline (plus, perhaps,
material which I sent to Linus today).

So please check all that against mainline in a day or so, refresh,
retest and resend.

Please separate the fix for the performance regression (1/5) into a
single standalone patch, ready for -stable backporting.  And then a
separate 4-patch series with the cleanups for a 5.11 merge.

Thanks.