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

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Date:   Mon, 24 Apr 2023 22:36:57 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Yang Shi <shy828301@...il.com>
Cc:     Luis Chamberlain <mcgrof@...nel.org>, hughd@...gle.com,
        akpm@...ux-foundation.org, brauner@...nel.org, djwong@...nel.org,
        p.raghav@...sung.com, da.gomez@...sung.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 2/8] shmem: convert to use folio_test_hwpoison()

On Mon, Apr 24, 2023 at 02:17:12PM -0700, Yang Shi wrote:
> On Fri, Apr 21, 2023 at 8:05 PM Luis Chamberlain <mcgrof@...nel.org> wrote:
> >
> > On Fri, Apr 21, 2023 at 11:42:53PM +0100, Matthew Wilcox wrote:
> > > On Fri, Apr 21, 2023 at 02:43:54PM -0700, Luis Chamberlain wrote:
> > > > The PageHWPoison() call can be converted over to the respective folio call
> > > > folio_test_hwpoison(). This introduces no functional changes.
> > >
> > > Um, no.  Nobody should use folio_test_hwpoison(), it's a nonsense.
> > >
> > > Individual pages are hwpoisoned.  You're only testing the head page
> > > if you use folio_test_hwpoison().  There's folio_has_hwpoisoned() to
> > > test if _any_ page in the folio is poisoned.  But blindly converting
> > > PageHWPoison to folio_test_hwpoison() is wrong.
> >
> > Thanks! I don't see folio_has_hwpoisoned() though.
> 
> We do have PageHasHWPoisoned(), which indicates at least one subpage
> is hwpoisoned in the huge page.
> 
> You may need to add a folio variant.

PAGEFLAG(HasHWPoisoned, has_hwpoisoned, PF_SECOND)
        TESTSCFLAG(HasHWPoisoned, has_hwpoisoned, PF_SECOND)

That generates folio_has_hwpoisoned() along with
folio_set_has_hwpoisoned(), folio_clear_has_hwpoisoned(),
folio_test_set_has_hwpoisoned() and folio_test_clear_has_hwpoisoned().