linux-kernel - Re: [PATCH v2 03/13] filemap: align the index to mapping_min

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Message-ID: <ofna2ao4w5aywviupntdz6m5xos6qb5btdxxixkyosfw45exwp@iuuexfq62qhr>
Date: Mon, 4 Mar 2024 16:36:34 +0100
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org, 
	djwong@...nel.org, mcgrof@...nel.org, linux-mm@...ck.org, hare@...e.de, 
	david@...morbit.com, akpm@...ux-foundation.org, gost.dev@...sung.com, 
	linux-kernel@...r.kernel.org, chandan.babu@...cle.com, Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH v2 03/13] filemap: align the index to mapping_min_order
 in the page cache

On Fri, Mar 01, 2024 at 07:26:55PM +0000, Matthew Wilcox wrote:
> On Fri, Mar 01, 2024 at 05:44:34PM +0100, Pankaj Raghav (Samsung) wrote:
> > +#define DEFINE_READAHEAD_ALIGNED(ractl, f, r, m, i)			\
> > +	struct readahead_control ractl = {				\
> > +		.file = f,						\
> > +		.mapping = m,						\
> > +		.ra = r,						\
> > +		._index = mapping_align_start_index(m, i),		\
> > +	}
> 
> My point was that you didn't need to do any of this.
> 
Got it. I probably didn't understand your old comment properly.

> Look, I've tried to give constructive review, but I feel like I'm going
> to have to be blunt.  There is no evidence of design or understanding
> in these patches or their commit messages.  You don't have a coherent
> message about "These things have to be aligned; these things can be at
> arbitrary alignment".  If you have thought about it, it doesn't show.
> 
> Maybe you just need to go back over the patches and read them as a series,
> but it feels like "Oh, there's a hole here, patch it; another hole here,
> patch it" without thinking about what's going on and why.
> 
> I want to help, but it feels like it'd be easier to do all the work myself
> at this point, and that's not good for me, and it's not good for you.
> 
> So, let's start off: Is the index in ractl aligned or not, and why do
> you believe that's the right approach?  And review each of the patches
> in this series with the answer to that question in mind because you are
> currently inconsistent.

Thanks for the feedback, and I get your comment about inconsistentency,
especially in the part where we align the index probably in places where
it doesn't even matter. As someone who is a bit new to the inner
workings of the page cache, I was a bit unsure about choosing the right
abstracation to enforce alignment.

I am going through all the patches now based on your feedback and
changing the commit messages to clarify the intent.

--
Pankaj