linux-kernel - Re: [PATCH v1 4/4] mm/mmu_gather: Store and process pages in contig ranges

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Message-ID: <ZO3+cQouje862QNu@casper.infradead.org>
Date:   Tue, 29 Aug 2023 15:19:29 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Ryan Roberts <ryan.roberts@....com>
Cc:     Will Deacon <will@...nel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Arnd Bergmann <arnd@...db.de>,
        David Hildenbrand <david@...hat.com>,
        Yu Zhao <yuzhao@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Yin Fengwei <fengwei.yin@...el.com>,
        Yang Shi <shy828301@...il.com>,
        "Huang, Ying" <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 4/4] mm/mmu_gather: Store and process pages in contig
 ranges

On Tue, Aug 29, 2023 at 03:02:22PM +0100, Ryan Roberts wrote:
> >> +			if (put_devmap_managed_page(&folio->page))
> >> +				continue;
> >> +			if (folio_put_testzero(folio))
> > 
> > We're only putting one ref for the zone_device folios?  Surely
> > this should be ref_sub_and_test like below?
> 
> Good point. This function is originally a copy/paste of release_pages(), and I
> obviously missed this. In fact, looking at it again today, I think I'll factor
> out the vast majority into a common helper, since I'm currently duplicating a
> whole bunch here.
> 
> In practice I think all devmap folios will be small today though? So while I
> agree I need to fix this, I think in practice it will currently do the right thing?

I think the devdax code uses 2MB folios.

> > You'll be glad to know I've factored out a nice little helper for that.
> 
> OK, what's it called? This is just copied from release_pages() at the moment.
> Happy to use your helper in the refactored common helper.

I'll send out those patches today.