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From:   Christoph Hellwig <hch@lst.de>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        Chris Wilson <chris@chris-wilson.co.uk>,
        Matthew Auld <matthew.auld@intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Minchan Kim <minchan@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        Nitin Gupta <ngupta@vflare.org>, x86@kernel.org,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-mm@kvack.org
Subject: [PATCH 04/11] mm: allow a NULL fn callback in apply_to_page_range
Date:   Thu, 24 Sep 2020 15:58:46 +0200
Message-Id: <20200924135853.875294-5-hch@lst.de>
In-Reply-To: <20200924135853.875294-1-hch@lst.de>
References: <20200924135853.875294-1-hch@lst.de>
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Besides calling the callback on each page, apply_to_page_range also has
the effect of pre-faulting all PTEs for the range.  To support callers
that only need the pre-faulting, make the callback optional.

Based on a patch from Minchan Kim <minchan@kernel.org>.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 mm/memory.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 469af373ae76e1..a60136046d7fcc 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2231,13 +2231,15 @@ static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
 
 	arch_enter_lazy_mmu_mode();
 
-	do {
-		if (create || !pte_none(*pte)) {
-			err = fn(pte++, addr, data);
-			if (err)
-				break;
-		}
-	} while (addr += PAGE_SIZE, addr != end);
+	if (fn) {
+		do {
+			if (create || !pte_none(*pte)) {
+				err = fn(pte++, addr, data);
+				if (err)
+					break;
+			}
+		} while (addr += PAGE_SIZE, addr != end);
+	}
 	*mask |= PGTBL_PTE_MODIFIED;
 
 	arch_leave_lazy_mmu_mode();
-- 
2.28.0