On 01/28/2013 02:26 PM, Pekka Enberg wrote:
> On Mon, Jan 28, 2013 at 1:24 PM, Jerome Marchand <jmarc...@redhat.com> wrote:
>> On 01/28/2013 08:16 AM, Pekka Enberg wrote:
>>> On Mon, Jan 28, 2013 at 2:38 AM, Minchan Kim <minc...@kernel.org> wrote:
>>>> Now zram allocates new page with GFP_KERNEL in zram I/O path
>>>> if IO is partial. Unfortunately, It may cuase deadlock with
>>>
>>> s/cuase/cause/g
>>>
>>>> reclaim path so this patch solves the problem.
>>>
>>> It'd be nice to know about the problem in more detail. I'm also
>>> curious on why you decided on GFP_ATOMIC for the read path and
>>> GFP_NOIO in the write path.
>>
>> This is because we're holding a kmap_atomic page in the read path.
>
> Okay, so that's about partial *reads* and not even mentioned in the
> changelog, no?
>
> AFAICT, you could rearrange the code in zram_bvec_read() as follows:
>
> if (is_partial_io(bvec))
> /* Use a temporary buffer to decompress the page */
> uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> else {
> uncmem = user_mem = kmap_atomic(page);
> }
>
> and avoid the GFP_ATOMIC allocation.
>
user_mem still has to be mapped in case of partial I/O too. But the
temporary buffer allocation could happen before. The allocation still
would need to be GFP_NOIO to avoid possible deadlocks.
Anyhow, the commit message could definitely be more explicit.
Regards,
Jerome
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