linux-kernel - Re: [RFC PATCH] f2fs: Convert f2fs_write_cache_pages() to use filemap_get_folios

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Date:   Thu, 15 Dec 2022 18:45:09 +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,
        fengnanchang@...il.com, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH] f2fs: Convert f2fs_write_cache_pages() to use
 filemap_get_folios_tag()

On Thu, Dec 15, 2022 at 09:48:41AM +0800, Chao Yu wrote:
> On 2022/12/13 3:13, Vishal Moola (Oracle) wrote:
> > +add_more:
> > +			pages[nr_pages] = folio_page(folio,idx);
> > +			folio_ref_inc(folio);
> 
> It looks if CONFIG_LRU_GEN is not set, folio_ref_inc() does nothing. For those
> folios recorded in pages array, we need to call folio_get() here to add one more
> reference on each of them?

static inline void folio_get(struct folio *folio)
{
        VM_BUG_ON_FOLIO(folio_ref_zero_or_close_to_overflow(folio), folio);
        folio_ref_inc(folio);
}

That said, folio_ref_inct() is very much MM-internal and filesystems
should be using folio_get(), so please make that modification in the
next revision, Vishal.