linux-kernel - Re: [PATCH v2] readahead: Correct the start and size in ondemand

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Date:   Wed, 5 Jul 2023 09:52:35 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     "Yin, Fengwei" <fengwei.yin@...el.com>, willy@...radead.org
Cc:     akpm@...ux-foundation.org, willy@...radead.org,
        ackerleytng@...gle.com, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        oliver.sang@...el.com
Subject: Re: [PATCH v2] readahead: Correct the start and size in
 ondemand_readahead()

On 07/04/23 09:41, Yin, Fengwei wrote:
> On 7/4/2023 2:49 AM, Mike Kravetz wrote:
> > On 06/28/23 12:43, Yin Fengwei wrote:
> > 
> > Thank you for your detailed analysis!
> > 
> > When the regression was initially discovered, I sent a patch to revert
> > commit 9425c591e06a.  Andrew has picked up this change.  And, Andrew has
> > also picked up this patch.
> Oh. I didn't notice that you sent revert patch. My understanding is that
> commit 9425c591e06a is a good change.
> 
> > 
> > I have not verified yet, but I suspect that this patch is going to cause
> > a regression because it depends on the behavior of page_cache_next_miss
> > in 9425c591e06a which has been reverted.
> Yes. If the 9425c591e06a was reverted, this patch could introduce regression.
> Which fixing do you prefer? reverting 9425c591e06a or this patch? Then we
> can suggest to Andrew to take it.

For now, I suggest we go with the revert.  Why?
- The revert is already going into stable trees.
- I may not be remembering correctly, but I seem to recall Matthew
  mentioning plans to redo/redesign the page cache and possibly
  readahead code.  If this is the case, then better to keep the legacy
  behavior for now.  But, I am not sure if this is actually part of any
  plan or work in progress.

-- 
Mike Kravetz