linux-kernel - Re: [RFC v2 2/8] shmem: convert to use is_folio

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Message-ID: <ZHD9Yi04AvbawW8d@casper.infradead.org>
Date:   Fri, 26 May 2023 19:41:38 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     hughd@...gle.com, akpm@...ux-foundation.org, brauner@...nel.org,
        djwong@...nel.org, p.raghav@...sung.com, da.gomez@...sung.com,
        rohan.puri@...sung.com, rpuri.linux@...il.com,
        a.manzanares@...sung.com, dave@...olabs.net, yosryahmed@...gle.com,
        keescook@...omium.org, hare@...e.de, kbusch@...nel.org,
        patches@...ts.linux.dev, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 2/8] shmem: convert to use is_folio_hwpoison()

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.