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mm: swap-token: add a comment for priority aging

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Document some swap token aging design decisions.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
KOSAKI Motohiro 2011-07-25 17:12:08 -07:00 committed by Linus Torvalds
parent 53bb01f593
commit 45ebb84025
1 changed files with 11 additions and 0 deletions
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11
mm/thrash.c
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@ -67,6 +67,17 @@ void grab_swap_token(struct mm_struct *mm)
if (!swap_token_mm)
goto replace_token;
/*
* Usually, we don't need priority aging because long interval faults
* makes priority decrease quickly. But there is one exception. If the
* token owner task is sleeping, it never make long interval faults.
* Thus, we need a priority aging mechanism instead. The requirements
* of priority aging are
* 1) An aging interval is reasonable enough long. Too short aging
* interval makes quick swap token lost and decrease performance.
* 2) The swap token owner task have to get priority aging even if
* it's under sleep.
*/
if ((global_faults - last_aging) > TOKEN_AGING_INTERVAL) {
swap_token_mm->token_priority /= 2;
last_aging = global_faults;