linux-kernel - Re: [PATCH v2] staging: zcache: support multiple clients, prep for KVM and RAMster

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Date:	Wed, 10 Aug 2011 10:40:42 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
CC:	Greg Kroah-Hartman <gregkh@...e.de>,
	Marcus Klemm <marcus.klemm@...glemail.com>,
	Konrad Wilk <konrad.wilk@...cle.com>,
	linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
	kvm@...r.kernel.org, linux-mm <linux-mm@...ck.org>,
	Brian King <brking@...ux.vnet.ibm.com>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2] staging: zcache: support multiple clients, prep for
 KVM and RAMster

On 08/10/2011 10:08 AM, Dan Magenheimer wrote:
>> From: Seth Jennings [mailto:sjenning@...ux.vnet.ibm.com]
>> Subject: Re: [PATCH v2] staging: zcache: support multiple clients, prep for KVM and RAMster
>>
>>> This crash is hit every time a high memory page is swapped out.
>>>
>>> I have no solution right now other that to revert this patch and
>>> restore the original signatures.
> 
> Hi Seth --
> 
> Thanks for your testing.  I haven't done much testing on 32-bit.
> 
>> Sorry for the noise, but I noticed right after I sent this that
>> the tmem layer doesn't DO anything with the data parameter. So
>> a possible solution is to just pass the page pointer instead of
>> the virtual address.  After all, pointers are pointers.
> 
> Yes, this looks like a good patch.
> 
>> --- a/drivers/staging/zcache/zcache.c
>> +++ b/drivers/staging/zcache/zcache.c
>> @@ -1153,7 +1153,7 @@ static void *zcache_pampd_create(char *data, size_t size,
>>         size_t clen;
>>         int ret;
>>         unsigned long count;
>> -       struct page *page = virt_to_page(data);
>> +       struct page *page = (struct page *)(data);
>>         struct zcache_client *cli = pool->client;
>>         uint16_t client_id = get_client_id_from_client(cli);
>>         unsigned long zv_mean_zsize;
>> @@ -1220,7 +1220,7 @@ static int zcache_pampd_get_data(char *data, size_t *bufsi
>>         int ret = 0;
>>
>>         BUG_ON(is_ephemeral(pool));
>> -       zv_decompress(virt_to_page(data), pampd);
>> +       zv_decompress((struct page *)(data), pampd);
>>         return ret;
>>  }
>>
>> @@ -1532,7 +1532,7 @@ static int zcache_put_page(int cli_id, int pool_id, struct
>>                 goto out;
>>         if (!zcache_freeze && zcache_do_preload(pool) == 0) {
>>                 /* preload does preempt_disable on success */
>> -               ret = tmem_put(pool, oidp, index, page_address(page),
>> +               ret = tmem_put(pool, oidp, index, (char *)(page),
>>                                 PAGE_SIZE, 0, is_ephemeral(pool));
>>                 if (ret < 0) {
>>                         if (is_ephemeral(pool))
>> @@ -1565,7 +1565,7 @@ static int zcache_get_page(int cli_id, int pool_id, struct
>>         pool = zcache_get_pool_by_id(cli_id, pool_id);
>>         if (likely(pool != NULL)) {
>>                 if (atomic_read(&pool->obj_count) > 0)
>> -                       ret = tmem_get(pool, oidp, index, page_address(page),
>> +                       ret = tmem_get(pool, oidp, index, (char *)(page),
>>                                         &size, 0, is_ephemeral(pool));
>>                 zcache_put_pool(pool);
>>         }
>>
>> I tested this and it works.
>>
>> Dan, does this mess anything else up?
> 
> Acked-by: Dan Magenheimer <dan.magenheimer@...cle.com>
> 
>>> What was the rationale for the signature changes?
>>> Seth
> 
> The change on the tmem side allows tmem to handle pre-compressed pages,
> which is useful to RAMster and possibly for KVM.  The new "raw"
> parameter identifies that case, but for zcache "raw" is always zero so
> your solution looks fine.
> 
> Seth, could you submit an "official" patch (i.e. proper subject field,
> signed-off-by) and I will ack that and ask GregKH to queue it up for
> a 3.1-rc?

Will do. I'm actually about to send out a set of 3 patches for zcache.
There is a Makefile issue, and a 32-bit link-time issue I have found
as well.  Hopefully, I'll send it out today.

> 
> Subject something like: staging: zcache: fix highmem crash on 32-bit
> 
> Thanks,
> Dan
> 
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