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Fri, 6 Mar 2026 16:04:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772813048; bh=rDwyViAwJBrWqHHIJBFX6WS4Aph53FS/v3jxwcha0Dg=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=NyRMpeAc4u6y1bOweC+oL1pis1n9yLFuTtLwnaUrYwqVmS04JztDPODWebMOjtgHG 8Fbr6g27cgQp5m17yZbh7JI8fGZ10S9y0Cr+pcX4HVLSzfam0/RHeiP22aiFXmTcSO m0JAkjjIdvcoeV0GjSXsbjx1PSem9FDJLdlR9l9XuQ7+JD77UCoo/+4blAoFrFHjtL 4lmP/E5Rc6HT7h8C6PmXHl7OCQQzJE8sLKpJ3BhxpLtIzac0pBDjbI8v8Sn+lsg4pM tBbGfrIkl+EK0Z5f0OcPdpEvn/ccg8GzXxJT1Z9Fkm2SnytuuVu3o7hx2RjZi50Rbj AaMG4PpMzZF8w== Message-ID: Date: Fri, 6 Mar 2026 17:03:57 +0100 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 11/13] mm/util: Add flag to track device private pages in page snapshots From: "David Hildenbrand (Arm)" To: Jordan Niethe , linux-mm@kvack.org Cc: balbirs@nvidia.com, matthew.brost@intel.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, ziy@nvidia.com, apopple@nvidia.com, lorenzo.stoakes@oracle.com, lyude@redhat.com, dakr@kernel.org, airlied@gmail.com, simona@ffwll.ch, rcampbell@nvidia.com, mpenttil@redhat.com, jgg@nvidia.com, willy@infradead.org, linuxppc-dev@lists.ozlabs.org, intel-xe@lists.freedesktop.org, jgg@ziepe.ca, Felix.Kuehling@amd.com, jhubbard@nvidia.com, maddy@linux.ibm.com, mpe@ellerman.id.au, ying.huang@linux.alibaba.com References: <20260202113642.59295-1-jniethe@nvidia.com> <20260202113642.59295-12-jniethe@nvidia.com> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/6/26 17:02, David Hildenbrand (Arm) wrote: > On 2/2/26 12:36, Jordan Niethe wrote: >> A future change will remove device private pages from the physical >> address space. This will mean that device private pages no longer have >> normal pfns and must be handled separately. >> >> Add a new flag PAGE_SNAPSHOT_DEVICE_PRIVATE to track when the pfn of a >> page snapshot is a device private page. >> >> Signed-off-by: Jordan Niethe >> Signed-off-by: Alistair Popple >> --- >> v1: >> - No change >> v2: >> - No change >> v3: >> - No change >> v4: >> - Move logical continuation to previous line >> --- >> fs/proc/page.c | 6 ++++-- >> include/linux/mm.h | 7 ++++--- >> mm/util.c | 3 +++ >> 3 files changed, 11 insertions(+), 5 deletions(-) >> >> diff --git a/fs/proc/page.c b/fs/proc/page.c >> index f9b2c2c906cd..bc14f7ebc369 100644 >> --- a/fs/proc/page.c >> +++ b/fs/proc/page.c >> @@ -191,10 +191,12 @@ u64 stable_page_flags(const struct page *page) >> folio_test_large_rmappable(folio)) { >> /* Note: we indicate any THPs here, not just PMD-sized ones */ >> u |= 1 << KPF_THP; >> - } else if (is_huge_zero_pfn(ps.pfn)) { >> + } else if (!(ps.flags & PAGE_SNAPSHOT_DEVICE_PRIVATE) && >> + is_huge_zero_pfn(ps.pfn)) { >> u |= 1 << KPF_ZERO_PAGE; >> u |= 1 << KPF_THP; >> - } else if (is_zero_pfn(ps.pfn)) { >> + } else if (!(ps.flags & PAGE_SNAPSHOT_DEVICE_PRIVATE) && >> + is_zero_pfn(ps.pfn)) { >> u |= 1 << KPF_ZERO_PAGE; >> } >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index f0d5be9dc736..a52979536a5e 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -4627,9 +4627,10 @@ static inline bool page_pool_page_is_pp(const struct page *page) >> } >> #endif >> >> -#define PAGE_SNAPSHOT_FAITHFUL (1 << 0) >> -#define PAGE_SNAPSHOT_PG_BUDDY (1 << 1) >> -#define PAGE_SNAPSHOT_PG_IDLE (1 << 2) >> +#define PAGE_SNAPSHOT_FAITHFUL (1 << 0) >> +#define PAGE_SNAPSHOT_PG_BUDDY (1 << 1) >> +#define PAGE_SNAPSHOT_PG_IDLE (1 << 2) >> +#define PAGE_SNAPSHOT_DEVICE_PRIVATE (1 << 3) >> >> struct page_snapshot { >> struct folio folio_snapshot; >> diff --git a/mm/util.c b/mm/util.c >> index 97cae40c0209..65e3f1a97d76 100644 >> --- a/mm/util.c >> +++ b/mm/util.c >> @@ -1218,6 +1218,9 @@ static void set_ps_flags(struct page_snapshot *ps, const struct folio *folio, >> >> if (folio_test_idle(folio)) >> ps->flags |= PAGE_SNAPSHOT_PG_IDLE; >> + >> + if (is_device_private_page(page)) >> + ps->flags |= PAGE_SNAPSHOT_DEVICE_PRIVATE; > > stable_page_flags() has access to the page and can simply test that instead? > Or maybe even better, if the pfn has no meaning, set it to 0 or -1, or anything that will make the other code just ignore it. -- Cheers, David