Re: [PATCH] f2fs: Support enhanced hot/cold data separation for f2fs

From: Matthew Wilcox <willy@infradead.org>
To: Luis Chamberlain <mcgrof@kernel.org>
Cc: "Pankaj Raghav" <p.raghav@samsung.com>,
	"Jaegeuk Kim" <jaegeuk@kernel.org>,
	"Yangtao Li" <frank.li@vivo.com>,
	chao@kernel.org, linux-f2fs-devel@lists.sourceforge.net,
	linux-kernel@vger.kernel.org, fengnanchang@gmail.com,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	vishal.moola@gmail.com,
	"Javier González" <javier.gonz@samsung.com>,
	"Adam Manzanares" <a.manzanares@samsung.com>
Subject: Re: [PATCH] f2fs: Support enhanced hot/cold data separation for f2fs
Date: Thu, 25 Jan 2024 20:47:39 +0000	[thread overview]
Message-ID: <ZbLI63UHBErD6_L2@casper.infradead.org> (raw)
In-Reply-To: <Y5D8wYGpp/95ShTV@bombadil.infradead.org>

On Wed, Dec 07, 2022 at 12:51:13PM -0800, Luis Chamberlain wrote:
> On Wed, Nov 30, 2022 at 03:18:41PM +0000, Matthew Wilcox wrote:
> > From a filesystem point of view, you need to ensure that you handle folios
> > larger than PAGE_SIZE correctly.  The easiest way is to spread the use
> > of folios throughout the filesystem.  For example, today the first thing
> > we do in f2fs_read_data_folio() is convert the folio back into a page.
> > That works because f2fs hasn't told the kernel that it supports large
> > folios, so the VFS won't create large folios for it.
> > 
> > It's a lot of subtle things.  Here's an obvious one:
> >                         zero_user_segment(page, 0, PAGE_SIZE);
> > There's a folio equivalent that will zero an entire folio.
> > 
> > But then there is code which assumes the number of blocks per page (maybe
> > not in f2fs?) and so on.  Every filesystem will have its own challenges.
> > 
> > One way to approach this is to just enable large folios (see commit
> > 6795801366da or 8549a26308f9) and see what breaks when you run xfstests
> > over it.  Probably quite a lot!
> 
> Me and Pankaj are very interested in helping on this front. And so we'll
> start to organize and talk every week about this to see what is missing.
> First order of business however will be testing so we'll have to
> establish a public baseline to ensure we don't regress. For this we intend
> on using kdevops so that'll be done first.
> 
> If folks have patches they want to test in consideration for folio /
> iomap enhancements feel free to Cc us :)
> 
> After we establish a baseline we can move forward with taking on tasks
> which will help with this conversion.

So ... it's been a year.  How is this project coming along?  There
weren't a lot of commits to f2fs in 2023 that were folio related.