Messages in this thread | | | Date | Wed, 7 Dec 2005 21:53:47 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH 01/16] mm: delayed page activation |
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On Wed, Dec 07, 2005 at 03:44:25PM +0300, Nikita Danilov wrote: > Wu Fengguang writes: > > Yes, it also increased the lifetimes by meaningful values: first re-accessed > > pages are prolonged more lifetime. Immediately removing them from inactive_list > > is basicly doing MRU eviction. > > Are you talking about CLOCK-pro here? I don't understand your statement > in the context of current VM: if the "first re-accessed" page was close > to the cold tail of the inactive list, and "second re-accessed" page was > close to the head of the inactive list, then life-time of second one is > increased by larger amount.
Sorry, I fail to mention that I'm comparing two pages that are read in at the same time, therefore they are in the same place in inactive_list. But their re-access time can be quite different.
There are roughly two kinds of reads: almost instantly and slowly forward. For the former one, read-in-time = first-access-time, unless for initial cache misses. The latter one is the original purpose of of the patch: to keep one chunk of read-ahead pages together, instead of let them littering throughout the lru list.
> > Delayed activation increased scanning activity, while immediate activation > > increased the locking activity. Early profiling data on a 2 CPU Xeon box showed > > that the delayed activation acctually cost less time. > > That's great, but current mark_page_accessed() has an important > advantage: the work is done by the process that accessed the page in > read/write path, or at page fault. By delegating activation to the VM > scanner, the burden of work is shifted to the innocent thread that > happened to trigger scanning during page allocation.
Thanks to notice it. It will happen in the direct page reclaim path. But I have just made interesting tests of the patch, in which direct page reclaims were reduced to zero. Till now I have no hint of why this is happening :)
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