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Date:   Fri, 26 May 2023 10:41:00 -0700
From:   Luis Chamberlain <mcgrof@kernel.org>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     hughd@google.com, akpm@linux-foundation.org, brauner@kernel.org,
        djwong@kernel.org, p.raghav@samsung.com, da.gomez@samsung.com,
        rohan.puri@samsung.com, rpuri.linux@gmail.com,
        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: <ZHDvLD3vwt11EYFg@bombadil.infradead.org>
References: <20230526075552.363524-1-mcgrof@kernel.org>
 <20230526075552.363524-3-mcgrof@kernel.org>
 <ZHDDFoXs51Be8FcZ@casper.infradead.org>
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Sender: Luis Chamberlain <mcgrof@infradead.org>
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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?

But I get the idea.

> After your patch, you can't read any of them.  You've effectively
> increased the blast radius of any hwerror, and I don't think that's an
> acceptable change.

I see, thanks! Will fix if we move forward with this.

  Luis