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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1u2zqk-00000003QUG-2tUM; Thu, 10 Apr 2025 21:54:19 +0000 Date: Thu, 10 Apr 2025 22:54:18 +0100 From: Matthew Wilcox To: Dan Williams Cc: David Hildenbrand , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, nvdimm@lists.linux.dev, Alison Schofield , Alexander Viro , Christian Brauner , Jan Kara , Andrew Morton , Alistair Popple , Christoph Hellwig Subject: Re: [PATCH v1] fs/dax: fix folio splitting issue by resetting old folio order + _nr_pages Message-ID: References: <20250410091020.119116-1-david@redhat.com> <67f826cbd874f_72052944e@dwillia2-xfh.jf.intel.com.notmuch> <67f82e0e234ea_720529471@dwillia2-xfh.jf.intel.com.notmuch> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <67f82e0e234ea_720529471@dwillia2-xfh.jf.intel.com.notmuch> X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: CB35D1C0005 X-Stat-Signature: eyetm4b9j9cyk7g4hx7ru9zwk1csjta5 X-HE-Tag: 1744322064-126615 X-HE-Meta: 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 rSp44qcM vaegBVmvenHCvLTXAslcZI7YKiNfal3WXwqbTnarVa3dLH44u+rs+jjyFXhr4AIaghbGyflDRvoY+IOTIjswIVWMXqtHCvTaJeNUrptcp21f70+YT1uSpDlBwE+C7tL0rAuClgEtZAPiyxIJf6gI4DXRVgUYSQ7ave5g27/TiSMikoZJc0OVzQK8xoKdjP4ne7+f/o9U+27lWnvafgVCvU0Ih0xMEh1kXEpJM956LvOuLBmYjPe4zamGifrUgK/ZjBe3pZT7HLDqFa/yhH9LkcC1u+w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Apr 10, 2025 at 01:46:06PM -0700, Dan Williams wrote: > Matthew Wilcox wrote: > > On Thu, Apr 10, 2025 at 01:15:07PM -0700, Dan Williams wrote: > > > For consistency and clarity what about this incremental change, to make > > > the __split_folio_to_order() path reuse folio_reset_order(), and use > > > typical bitfield helpers for manipulating _flags_1? > > > > I dislike this intensely. It obfuscates rather than providing clarity. > > I'm used to pushing folks to use bitfield.h in driver land, but will not > push it further here. I think it can make sense in places. Just not here. > What about this hunk? > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 2a47682d1ab7..301ca9459122 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3404,7 +3404,7 @@ static void __split_folio_to_order(struct folio *folio, int old_order, > if (new_order) > folio_set_order(folio, new_order); > else > - ClearPageCompound(&folio->page); > + folio_reset_order(folio); > } I think that's wrong. We're splitting this folio into order-0 folios, but folio_reset_order() is going to modify folio->_flags_1 which is in the next page.