Re: [Bug 192571] zswap + zram enabled BUG

[Dan Streetman <ddstreet@ieee.org>]

On Tue, Jan 24, 2017 at 11:02 PM, Chulmin Kim <cmlaika.kim@samsung.com> wrote:
> On 01/24/2017 03:16 PM, Dan Streetman wrote:
>>
>> On Mon, Jan 23, 2017 at 7:03 PM, Alexandr <sss123next@list.ru> wrote:
>>>
>>> -----BEGIN PGP SIGNED MESSAGE-----
>>> Hash: SHA512
>>>
>>>
>>>> Why would you do this?  There's no benefit of using zswap together
>>>> with zram.
>>>
>>>
>>> i just wanted to test zram and zswap, i still not dig to deep in it,
>>> but what i wanted is to use zram swap (with zswap disabled), and if it
>>> exceeded use real swap on block device with zswap enabled.
>>
>>
>> I don't believe that's possible, you can't enable zswap for only
>> specific swap devices; and anyway, if you fill up zram, you won't
>> really have any memory left for zswap to use will you?
>>
>> However, it shouldn't encounter any BUG(), like you saw.  If it's
>> reproducable for you, can you give details on how to reproduce it?
>>
>
> Hello. Mr. Streetman.
>
>
> Regarding to this problem, I have a question on zswap.
>
> Is there any reason that
> zswap_frontswap_load() does not call flush_dcache_page()?
>
> The zswap load function can dirty the page mapped to user space (might be
> shareable/writable) which seems exactly the condition mentioned in the
> definition of flush_dcache_page().
>
> I'm thinking that
> flush_dcache_page() should be called in the end of zswap_frontswap_load().
> Could you review my opinion?

I don't think it needs to, as i detailed in my response to the other thread.

Also, this is a different issue, I think - even if there is a cache
problem with pages loaded from zswap, i don't see how it would cause a
decompression failure - the zpool storage is the only code that has a
copy of its compressed pages, no userspace or any other kernel code
should be accessing any of it.

>
> Thanks!
> Chulmin Kim
>
>
>
>
>
>
>
>
>
>> --
>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>> the body to majordomo@kvack.org.  For more info on Linux MM,
>> see: http://www.linux-mm.org/ .
>> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
>>
>>
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
>

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>