linux-kernel - Re: [PATCH v2 12/12] mm/filemap: Return only head pages from find_get

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Message-ID: <20200930170807.GA15977@quack2.suse.cz>
Date:   Wed, 30 Sep 2020 19:08:07 +0200
From:   Jan Kara <jack@...e.cz>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Jan Kara <jack@...e.cz>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        William Kucharski <william.kucharski@...cle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Dave Chinner <dchinner@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 12/12] mm/filemap: Return only head pages from
 find_get_entries

On Wed 30-09-20 13:36:37, Matthew Wilcox wrote:
> On Wed, Sep 30, 2020 at 02:15:12PM +0200, Jan Kara wrote:
> > On Mon 14-09-20 14:00:42, Matthew Wilcox (Oracle) wrote:
> > > All callers now expect head (and base) pages, and can handle multiple
> > > head pages in a single batch, so make find_get_entries() behave that way.
> > > Also take the opportunity to make it use the pagevec infrastructure
> > > instead of open-coding how pvecs behave.  This has the side-effect of
> > > being able to append to a pagevec with existing contents, although we
> > > don't make use of that functionality anywhere yet.
> > > 
> > > Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> > 
> > Looks good to me. You can add:
> > 
> > Reviewed-by: Jan Kara <jack@...e.cz>
> > 
> > I'm just curious: What has happened to pagevec_lookup_entries() call in
> > invalidate_inode_pages2_range()? Your series appears to be based on a tree
> > where the call already does not exist...
> 
> That went away in patch 10 of this series.

Ah, I see. Thanks. Then I'm somewhat wondering is really
invalidate_inode_pages2_range() safe for THP head pages? At least the:

	unmap_mapping_pages(mapping, index, 1, false);

doesn't look adequate for THP head pages... do_launder_page() is also
doubtful but probably currently OK because THPs cannot be dirty at this
moment. But how about THPs that are partialy inside start-end range? So far
the function didn't care because it was operating on page basis so it
didn't care but now it is probably relevant... At least it would warrant a
comment in some changelog if you are convinced everything is safe.

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR