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Date:   Fri, 26 May 2023 19:41:38 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Luis Chamberlain <mcgrof@kernel.org>
Cc:     hughd@google.com, akpm@linux-foundation.org, brauner@kernel.org,
        djwong@kernel.org, p.raghav@samsung.com, da.gomez@samsung.com,
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        a.manzanares@samsung.com, dave@stgolabs.net, yosryahmed@google.com,
        keescook@chromium.org, hare@suse.de, kbusch@kernel.org,
        patches@lists.linux.dev, linux-block@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC v2 2/8] shmem: convert to use is_folio_hwpoison()
Message-ID: <ZHD9Yi04AvbawW8d@casper.infradead.org>
References: <20230526075552.363524-1-mcgrof@kernel.org>
 <20230526075552.363524-3-mcgrof@kernel.org>
 <ZHDDFoXs51Be8FcZ@casper.infradead.org>
 <ZHDvLD3vwt11EYFg@bombadil.infradead.org>
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On Fri, May 26, 2023 at 10:41:00AM -0700, Luis Chamberlain wrote:
> On Fri, May 26, 2023 at 03:32:54PM +0100, Matthew Wilcox wrote:
> > On Fri, May 26, 2023 at 12:55:46AM -0700, Luis Chamberlain wrote:
> > > The PageHWPoison() call can be converted over to the respective folio
> > > call is_folio_hwpoison(). This introduces no functional changes.
> > 
> > Yes, it very much does!
> > 
> > > @@ -4548,7 +4548,7 @@ struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
> > >  		return &folio->page;
> > >  
> > >  	page = folio_file_page(folio, index);
> > > -	if (PageHWPoison(page)) {
> > > +	if (is_folio_hwpoison(folio)) {
> > >  		folio_put(folio);
> > 
> > Imagine you have an order-9 folio and one of the pages in it gets
> > HWPoison.  Before, you can read the other 511 pages in the folio.
> 
> But before we didn't use high order folios for reads on tmpfs?

Sure we did!  If SHMEM_HUGE_ALWAYS is set, we can see reads of THPs
(order-9 folios) in this path.