Re: [PATCH v2] mm/zswap: change zswap to writethrough cache

[Weijie Yang <weijie.yang.kh@gmail.com>]

Hello Dan,

On Thu, Nov 21, 2013 at 8:42 AM, Bob Liu <bob.liu@oracle.com> wrote:
> Hi Dan,
>
> On 11/21/2013 03:49 AM, Dan Streetman wrote:
>> Currently, zswap is writeback cache; stored pages are not sent
>> to swap disk, and when zswap wants to evict old pages it must
>> first write them back to swap cache/disk manually.  This avoids
>> swap out disk I/O up front, but only moves that disk I/O to
>> the writeback case (for pages that are evicted), and adds the
>> overhead of having to uncompress the evicted pages, and adds the
>> need for an additional free page (to store the uncompressed page)
>> at a time of likely high memory pressure.  Additionally, being
>> writeback adds complexity to zswap by having to perform the
>> writeback on page eviction.
>>
>
> Good work!
>
>> This changes zswap to writethrough cache by enabling
>> frontswap_writethrough() before registering, so that any
>> successful page store will also be written to swap disk.  All the
>> writeback code is removed since it is no longer needed, and the
>> only operation during a page eviction is now to remove the entry
>> from the tree and free it.
>>

Thanks for your work. I reviewed this patch, and it is good to me.

However, I am skeptical about it because:
1. it will add more IO than original zswap, how does it result in a
performance improvement ?
2. most embedded device use NAND, more IO will reduce its working life

Regards

> Could you do some testing using eg. SPECjbb? And compare the result with
> original zswap.
>
> Thanks,
> -Bob
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

--
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>