Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Baoquan He <bhe@redhat.com>
To:     linux-mm@kvack.org
Cc:     linux-kernel@vger.kernel.org, urezki@gmail.com, lstoakes@gmail.com,
        stephen.s.brennan@oracle.com, willy@infradead.org,
        akpm@linux-foundation.org, hch@infradead.org,
        Baoquan He <bhe@redhat.com>
Subject: [PATCH v3 5/7] mm/vmalloc: skip the uninitilized vmalloc areas
Date:   Fri, 13 Jan 2023 11:19:19 +0800
Message-Id: <20230113031921.64716-6-bhe@redhat.com>
In-Reply-To: <20230113031921.64716-1-bhe@redhat.com>
References: <20230113031921.64716-1-bhe@redhat.com>
MIME-Version: 1.0
Content-type: text/plain
Content-Transfer-Encoding: 8bit
Precedence: bulk

For areas allocated via vmalloc_xxx() APIs, it searches for unmapped area
to reserve and allocates new pages to map into, please see function
__vmalloc_node_range(). During the process, flag VM_UNINITIALIZED is set
in vm->flags to indicate that the pages allocation and mapping haven't
been done, until clear_vm_uninitialized_flag() is called to clear it.

For this kind of area, if VM_UNINITIALIZED is still set, let's ignore
it in vread() because pages newly allocated and being mapped in that
area only contains zero data. reading them out by aligned_vread() is
wasting time.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 mm/vmalloc.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 4a10b3b692fa..dbcdcad2276b 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3660,6 +3660,11 @@ long vread(char *buf, char *addr, unsigned long count)
 		if (!vm && !flags)
 			continue;
 
+		if (vm && (vm->flags & VM_UNINITIALIZED))
+			continue;
+		/* Pair with smp_wmb() in clear_vm_uninitialized_flag() */
+		smp_rmb();
+
 		vaddr = (char *) va->va_start;
 		size = vm ? get_vm_area_size(vm) : va_size(va);
 
-- 
2.34.1