Re: [PATCH 0/3] VM throttling: avoid blocking occasional writers
From: Tomoki Sekiyama
Date: Mon Mar 26 2007 - 06:32:20 EST
Hi,
Thanks for your reply.
>>3) Use "dirty_ratio" as the blocking ratio. And add
>> "start_writeback_ratio", and start writeback at
>> start_writeback_ratio(default:90) * dirty_ratio / 100 [%].
>> In this way, specifying blocking ratio can be done in the same way
>> as current kernel, but high/low watermark algorithm is enabled.
>I like 3 better, it should make tuning behavior more precise.
Then, what do you think of the following idea?
(4) add `dirty_start_writeback_ratio' as percentage of memory,
at which a generator of dirty pages itself starts writeback
(that is, non-blocking ratio).
In this way, `dirty_ratio' is used as the blocking ratio, so we don't
need to modify the sysctl.conf etc. I think it's easier to understand
for administrators of systems, because the interface is similar as
`dirty_background_ratio' and`dirty_ratio.'
If this is OK, I'll repost the patch.
> You can make an argument for absolute values for writeback,
> if my disk will only write 70MB/s I may only want 203 sec of
> pending writes, regardless of available memory.
To realize tuning with absolute values, I consider that we need to
modify handling of `dirty_background_ratio,' `dirty_ratio' and so on as
well as `dirty_start_writeback_ratio.' I think this should be done in
another patch if this feature is required.
Regards,
--
Tomoki Sekiyama
Hitachi, Ltd., Systems Development Laboratory
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