Re: [RESEND PATCH v5 1/4] zram: Fix deadlock bug in partial write

[Pekka Enberg]

On Mon, Jan 28, 2013 at 1:24 PM, Jerome Marchand <jmarchan@xxxxxxxxxx> wrote:
> On 01/28/2013 08:16 AM, Pekka Enberg wrote:
>> On Mon, Jan 28, 2013 at 2:38 AM, Minchan Kim <minchan@xxxxxxxxxx> 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.
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