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From:   David Howells <dhowells@redhat.com>
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References: <Y3Lbul7FZncNVwVZ@codewreck.org> <166844174069.1124521.10890506360974169994.stgit@warthog.procyon.org.uk>
To:     Dominique Martinet <asmadeus@codewreck.org>
Cc:     dhowells@redhat.com, willy@infradead.org, dwysocha@redhat.com,
        Rohith Surabattula <rohiths.msft@gmail.com>,
        Steve French <sfrench@samba.org>,
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        Ilya Dryomov <idryomov@gmail.com>, linux-cachefs@redhat.com,
        linux-cifs@vger.kernel.org, linux-afs@lists.infradead.org,
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        linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
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Subject: Re: [RFC PATCH v2] mm, netfs, fscache: Stop read optimisation when folio removed from pagecache
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Date:   Tue, 15 Nov 2022 00:41:02 +0000
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Dominique Martinet <asmadeus@codewreck.org> wrote:

> any harm in setting this if netfs isn't enabled?
> (just asking because you checked in fs/9p/cache.c above)

Well, it forces a call to ->release_folio() every time a folio is released=
, if
set, rather than just if PG_private/PG_private_2 is set.

> > +static inline void mapping_clear_release_always(struct address_space =
*mapping)
> > +{
> > +	set_bit(AS_RELEASE_ALWAYS, &mapping->flags);
> =

> clear_bit certainly?

Bah.  Yes.

> > -	if (folio_has_private(folio) && !filemap_release_folio(folio, 0))
> > +	if (!filemap_release_folio(folio, 0))
> =

> should this (and all others) check for folio_needs_release instead of ha=
s_private?
> filemap_release_folio doesn't check as far as I can see, but perhaps
> it's already fast and noop for another reason I didn't see.

Willy suggested merging the checks from folio_has_private() into
filemap_release_folio():

	https://lore.kernel.org/r/Yk9V/03wgdYi65Lb@casper.infradead.org/

David