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Date:   Mon, 26 Sep 2022 08:46:15 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     yong w <yongw.pur@gmail.com>
Cc:     jaewon31.kim@samsung.com, linux-kernel@vger.kernel.org,
        mhocko@kernel.org, stable@vger.kernel.org, wang.yong12@zte.com.cn,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Minchan Kim <minchan@kernel.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH v2 stable-4.19 1/3] mm/page_alloc: use ac->high_zoneidx
 for classzone_idx
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On Sun, Sep 25, 2022 at 10:32:32PM +0800, yong w wrote:
> Greg KH <gregkh@linuxfoundation.org> 于2022年9月25日周日 19:00写道：
> >
> > On Sun, Sep 25, 2022 at 03:35:27AM -0700, wangyong wrote:
> > > From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> > >
> > > [ backport of commit 3334a45eb9e2bb040c880ef65e1d72357a0a008b ]
> >
> > This is from 5.8.  What about the 5.4.y kernel?  Why would someone
> > upgrading from 4.19.y to 5.4.y suffer a regression here?
> >
> I encountered this problem on 4.19, but I haven't encountered it on 5.4.
> However, this should be a common problem, so 5.4 may also need to be
> merged.
> 
> Hello, Joonsoo, what do you think?
> 
> > And why wouldn't someone who has this issue just not use 5.10.y instead?
> > What prevents someone from moving off of 4.19.y at this point in time?
> >
> This is a solution, but upgrading the kernel version requires time and overhead,
> so use the patch is the most effective way, if there is.

You will have to move off of 4.19 soon anyway, so why delay the change?

thanks,

greg k-h