Re: ~500 megs cached yet 2.6.5 goes into swap hell

[Nick Piggin]

Nikita Danilov wrote:

> Here are results that I obtained some time ago. Test is to concurrently
> clone (bk) and build (make -jN) kernel source in M directories.
>
> For N = M = 11, TIMEFORMAT='%3R %3S %3U'
>
>                                         REAL    SYS      USER
> "stock"                               3818.320 568.999 4358.460
> transfer-dirty-on-refill              3368.690 569.066 4377.845
> check-PageSwapCache-after-add-to-swap 3237.632 576.208 4381.248
> dont-unmap-on-pageout                 3207.522 566.539 4374.504
> async-writepage                       3115.338 562.702 4325.212

I like your transfer-dirty-on-refill change. It is definitely
worthwhile to mark a page as dirty when it drops off the active
list in order to hopefully get it written before it reaches the
tail of the inactive list.

> (check-PageSwapCache-after-add-to-swap was added to mainline since them.)
>
> These patches weren't updated for some time. Last version is at
> ftp://ftp.namesys.com/pub/misc-patches/unsupported/extra/2004.03.25-2.6.5-rc2
>
> [from Nick Piggin's patch]
>  > 
>  > Changes mark_page_accessed to only set the PageAccessed bit, and
>  > not move pages around the LRUs. This means we don't have to take
>  > the lru_lock, and it also makes page ageing and scanning consistient
>  > and all handled in mm/vmscan.c
>
> By the way, batch-mark_page_accessed patch at the URL above also tries
> to reduce lock contention in mark_page_accessed(), but through more
> standard approach of batching target pages in per-cpu pvec.

This is a good patch too if mark_page_accessed is required to
take the lock (which it currently is, of course).
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