Hello,
On 03/25/2015 12:24 AM, Sergey Senozhatsky wrote:
> object may belong to different pages. zs_object_copy() handles
> this case and maps a new source page (get_next_page() and
> kmap_atomic()) when object crosses boundaries of the current
> source page. But it also performs unnecessary kunmap/kmap_atomic
> of the destination page (it remains unchanged), which can be
> avoided.
No, it's not unnecessary. We should do kunmap_atomic() in the reverse
order of kmap_atomic(), so unfortunately it's inevitable to
kunmap_atomic() both on d_addr and s_addr.
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> ---
> mm/zsmalloc.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index d920e8b..7af4456 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1536,12 +1536,10 @@ static void zs_object_copy(unsigned long src, unsigned long dst,
> break;
>
> if (s_off + size >= PAGE_SIZE) {
> - kunmap_atomic(d_addr);
> kunmap_atomic(s_addr);
Removing kunmap_atomic(d_addr) here may cause BUG_ON() at __kunmap_atomic().
I tried yours to see it really happens:
> kernel BUG at arch/arm/mm/highmem.c:113!
> Internal error: Oops - BUG: 0 [#1] SMP ARM
> Modules linked in:
> CPU: 2 PID: 1774 Comm: bash Not tainted 4.0.0-rc2-mm1+ #105
> Hardware name: ARM-Versatile Express
> task: ee971300 ti: e8a26000 task.ti: e8a26000
> PC is at __kunmap_atomic+0x144/0x14c
> LR is at zs_object_copy+0x19c/0x2dc
regards
heesub
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