linux-kernel - Re: [PATCH RFC] fs: erofs: support PG_mappedtodisk flag for folios with zero-filled

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Message-ID: <CAGsJ_4yLK3sCeJNdZRKxD2tSdMVFRBp9eq-1mAMu7UT=gqpA_Q@mail.gmail.com>
Date: Thu, 17 Oct 2024 21:09:48 +1300
From: Barry Song <21cnbao@...il.com>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>
Cc: xiang@...nel.org, chao@...nel.org, linux-erofs@...ts.ozlabs.org, 
	huyue2@...lpad.com, jefflexu@...ux.alibaba.com, dhavale@...gle.com, 
	linux-kernel@...r.kernel.org, Barry Song <v-songbaohua@...o.com>
Subject: Re: [PATCH RFC] fs: erofs: support PG_mappedtodisk flag for folios
 with zero-filled

On Thu, Oct 17, 2024 at 9:00 PM Gao Xiang <hsiangkao@...ux.alibaba.com> wrote:
>
>
>
> On 2024/10/17 15:58, Gao Xiang wrote:
> > Hi Barry,
> >
> > On 2024/10/17 15:43, Barry Song wrote:
> >> From: Barry Song <v-songbaohua@...o.com>
> >>
> >> When a folio has never been zero-filled, mark it as mappedtodisk
> >> to allow other software components to recognize and utilize the
> >> flag.
> >>
> >> Signed-off-by: Barry Song <v-songbaohua@...o.com>
> >
> > Thanks for this!
> >
> > It looks good to me as an improvement as long as PG_mappedtodisk
> > is long-term lived and useful to users.
> >
> > Reviewed-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
>

thanks!

> BTW, I wonder if iomap supports this since uncompressed EROFS
> relies on iomap paths...

In the core layer, I only see fs/buffer.c's block_read_full_folio()
and fs/mpage.c's mpage_readahead() and mpage_readahead()
supporting this. I haven't found any code in iomap that sets the
flag.

I guess erofs doesn't call the above functions for non-compressed
files?

>
> Thanks,
> Gao Xiang

Barry