Re: [Qemu-devel] [PATCH v3 10/10] XBZRLE: update the doc of XBZRLE

[Eric Blake]

On 03/18/2014 06:24 AM, address@hidden wrote:
> From: ChenLiang <address@hidden>
> 
> update the doc of XBZRLE

Having the subject line and the body of the commit message be identical
is redundant.  And just by looking at the commit message, I can't see
WHY you are updating things.  If you were to keep this as a separate
commit, I'd suggest it look more like:

XBZRLE: document cache miss policy

Add a section to the XBZRLE documentation describing how the page cache
determines which pages are hot.


That said, I think you should squash this documentation update into
patch 5/10 where you actually implement it, so that a single patch
becomes self-documenting why you went with this design.  At which point,
the combined patch commit message should look something like:

XBZRLE: optimize XBZRLE to decrease cache misses

...existing text from 5/10...

Additionally, document the new cache age policy.

> 
> Signed-off-by: ChenLiang <address@hidden>
> Signed-off-by: Gonglei <address@hidden>
> ---
>  docs/xbzrle.txt | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/docs/xbzrle.txt b/docs/xbzrle.txt
> index cc3a26a..cdf1e3e 100644
> --- a/docs/xbzrle.txt
> +++ b/docs/xbzrle.txt
> @@ -71,6 +71,13 @@ encoded buffer:
>  encoded length 24
>  e9 07 0f 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 03 01 67 01 01 69
>  
> +The strategy of updating cache
> +=================================

Copy-and-paste from bad examples already in this file, but it's nicer
when the length of ==== matches the heading it is paired with.

> +Keeping the hot page in cache is effective to decrease cache missing.
> +XBZRLE use a counter as the age of page. The counter will increase
> +after the ram dirty bitmap syncing. When cache conflicts XBZRLE only
> +replace the old page in cache.

Suggestions for better grammar:

Cache update strategy
=====================
Keeping the hot pages in the cache is effective for decreased cache
misses. XBZRLE uses a counter as the age of each page. The counter will
increase after each ram dirty bitmap sync. When a cache conflict is
detected, XBZRLE will only evict pages in the cache that are older than
a threshold.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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