Messages in this thread | | | Date | Sun, 14 Mar 2004 12:15:03 -0800 | From | Andrew Morton <> | Subject | Re: [2.4] heavy-load under swap space shortage |
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Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote: > > At first I was skeptic to the inclusion of this patch in v2.4 (due to the > freeze), but after thinking a bit more about I have a few points in favour > of this modification (read Nomura's message below and the patch to know > what I'm talking about): > > - It is off by default > - It is very simple (non intrusive), it just changes the point in which > anonymous pages are inserted into the LRU. > - When turned on, I dont see it being a reason for introducing new > bugs. > > What you think of this?
hm, I hadn't noticed that 2.4 was changed to _not_ add anon pages to the LRU. I'd always regarded that as a workaround for pagemap_lru_lock contention on large SMP machines which would never get beyond the suse kernel.
Having a magic knob is a weak solution: the majority of people who are affected by this problem won't know to turn it on.
I confess that I don't really understand the failure mode. So we have zillions of anon pages which are not on the LRU. We call swap_out() and scan all these pages, failing to find swapcache space for them.
Why does adding the pages to the LRU up-front solve the problem?
(And why cannot we lazily add these anon pages to the LRU in swap_out, and avoid the need for the knob?)
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