Re: [PATCH v2 1/3] vmalloc: Choose a better start address in vm_area_register_early()
From: Kefeng Wang
Date: Thu Aug 05 2021 - 08:46:26 EST
On 2021/8/4 19:14, Catalin Marinas wrote:
On Mon, Aug 02, 2021 at 10:39:04AM +0800, Kefeng Wang wrote:
On 2021/8/1 23:23, Catalin Marinas wrote:
On Tue, Jul 20, 2021 at 10:51:03AM +0800, Kefeng Wang wrote:
There are some fixed locations in the vmalloc area be reserved
in ARM(see iotable_init()) and ARM64(see map_kernel()), but for
pcpu_page_first_chunk(), it calls vm_area_register_early() and
choose VMALLOC_START as the start address of vmap area which
could be conflicted with above address, then could trigger a
BUG_ON in vm_area_add_early().
Let's choose the end of existing address range in vmlist as the
start address instead of VMALLOC_START to avoid the BUG_ON.
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
mm/vmalloc.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d5cd52805149..a98cf97f032f 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2238,12 +2238,14 @@ void __init vm_area_add_early(struct vm_struct *vm)
*/
void __init vm_area_register_early(struct vm_struct *vm, size_t align)
{
- static size_t vm_init_off __initdata;
+ unsigned long vm_start = VMALLOC_START;
+ struct vm_struct *tmp;
unsigned long addr;
- addr = ALIGN(VMALLOC_START + vm_init_off, align);
- vm_init_off = PFN_ALIGN(addr + vm->size) - VMALLOC_START;
+ for (tmp = vmlist; tmp; tmp = tmp->next)
+ vm_start = (unsigned long)tmp->addr + tmp->size;
+ addr = ALIGN(vm_start, align);
vm->addr = (void *)addr;
vm_area_add_early(vm);
Is there a risk of breaking other architectures? It doesn't look like to
me but I thought I'd ask.
Before this patch, vm_init_off is to record the offset from VMALLOC_START,
but it use VMALLOC_START as start address on the function
vm_area_register_early()
called firstly, this will cause the BUG_ON.
With this patch, the most important change is that we choose the start
address via
dynamic calculate the 'start' address by traversing the list.
[wkf@localhost linux-next]$ git grep vm_area_register_early
arch/alpha/mm/init.c: vm_area_register_early(&console_remap_vm, PAGE_SIZE);
arch/x86/xen/p2m.c: vm_area_register_early(&vm, PMD_SIZE *
PMDS_PER_MID_PAGE);
mm/percpu.c: vm_area_register_early(&vm, PAGE_SIZE);
[wkf@localhost linux-next]$ git grep vm_area_add_early
arch/arm/mm/ioremap.c: vm_area_add_early(vm);
arch/arm64/mm/mmu.c: vm_area_add_early(vma);
x86/alpha won't call vm_area_add_early(), only arm64 could call both vm_area_add_early()
and vm_area_register_early() when this patchset is merged. so it won't break other architectures.
Thanks for checking.
Also, instead of always picking the end, could we search for a range
that fits?
We only need a space in vmalloc range, using end or a range in the middle
is not different.
I was thinking of making it more future-proof in case one registers a
vm area towards the end of the range. It's fairly easy to pick a range
in the middle now that you are adding a list traversal.
ok, will chose a suitable hole in the vmalloc range.