linux-kernel - Re: [f2fs-dev] [PATCH v3 14/23] f2fs: Convert f2fs_write_cache_pages() to use filemap_get_folios

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Date:   Tue, 29 Nov 2022 19:14:13 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Chao Yu <chao@...nel.org>
Cc:     "Vishal Moola (Oracle)" <vishal.moola@...il.com>,
        linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, linux-mm@...ck.org,
        fengnan chang <fengnanchang@...il.com>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [f2fs-dev] [PATCH v3 14/23] f2fs: Convert
 f2fs_write_cache_pages() to use filemap_get_folios_tag()

On Mon, Nov 14, 2022 at 03:02:34PM +0800, Chao Yu wrote:
> On 2022/10/18 4:24, Vishal Moola (Oracle) wrote:
> > Converted the function to use a folio_batch instead of pagevec. This is in
> > preparation for the removal of find_get_pages_range_tag().
> > 
> > Also modified f2fs_all_cluster_page_ready to take in a folio_batch instead
> > of pagevec. This does NOT support large folios. The function currently
> 
> Vishal,
> 
> It looks this patch tries to revert Fengnan's change:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=01fc4b9a6ed8eacb64e5609bab7ac963e1c7e486
> 
> How about doing some tests to evaluate its performance effect?
> 
> +Cc Fengnan Chang

Thanks for reviewing this.  I think the real solution to this is
that f2fs should be using large folios.  That way, the page cache
will keep track of dirtiness on a per-folio basis, and if your folios
are at least as large as your cluster size, you won't need to do the
f2fs_prepare_compress_overwrite() dance.  And you'll get at least fifteen
dirty folios per call instead of fifteen dirty pages, so your costs will
be much lower.

Is anyone interested in doing the work to convert f2fs to support
large folios?  I can help, or you can look at the work done for XFS,
AFS and a few other filesystems.