[patch] swapin rlimit

Ingo Molnar
2005-11-04T07:26:28Z

* Andrew Morton <akpm@osdl.org> wrote:

> Similarly, that SGI patch which was rejected 6-12 months ago to kill
> off processes once they started swapping. We thought that it could be
> done from userspace, but we need a way for userspace to detect when a
> task is being swapped on a per-task basis.

wouldnt the clean solution here be a "swap ulimit"?

I.e. something like the 2-minute quick-hack below (against Linus-curr).

Ingo

---
implement a swap ulimit: RLIMIT_SWAP.

setting the ulimit to 0 causes any swapin activity to kill the task.
Setting the rlimit to 0 is allowed for unprivileged users too, since it
is a decrease of the default RLIM_INFINITY value. I.e. users could run
known-memory-intense jobs with such an ulimit set, and get a guarantee
that they wont put the system into a swap-storm.

Note: it's just swapin that causes the SIGKILL, because at swapout time
it's hard to identify the originating task. Pure swapouts and a buildup
in the swap-cache is not punished, only actual hard swapins. I didnt try
too hard to make the rlimit particularly finegrained - i.e. right now we
only know 'zero' and 'infinity' ...

Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/asm-generic/resource.h | 4 +++-
mm/memory.c | 13 +++++++++++++
2 files changed, 16 insertions(+), 1 deletion(-)

Index: linux/include/asm-generic/resource.h
===================================================================
--- linux.orig/include/asm-generic/resource.h
+++ linux/include/asm-generic/resource.h
@@ -44,8 +44,9 @@
#define RLIMIT_NICE 13 /* max nice prio allowed to raise to
0-39 for nice level 19 .. -20 */
#define RLIMIT_RTPRIO 14 /* maximum realtime priority */
+#define RLIMIT_SWAP 15 /* maximum swapspace for task */

-#define RLIM_NLIMITS 15
+#define RLIM_NLIMITS 16

/*
* SuS says limits have to be unsigned.
@@ -86,6 +87,7 @@
[RLIMIT_MSGQUEUE] = { MQ_BYTES_MAX, MQ_BYTES_MAX }, \
[RLIMIT_NICE] = { 0, 0 }, \
[RLIMIT_RTPRIO] = { 0, 0 }, \
+ [RLIMIT_SWAP] = { RLIM_INFINITY, RLIM_INFINITY }, \
}

#endif /* __KERNEL__ */
Index: linux/mm/memory.c
===================================================================
--- linux.orig/mm/memory.c
+++ linux/mm/memory.c
@@ -1647,6 +1647,18 @@ void swapin_readahead(swp_entry_t entry,
}

/*
+ * Crude first-approximation swapin-avoidance: if there is a zero swap
+ * rlimit then kill the task.
+ */
+static inline void check_swap_rlimit(void)
+{
+ unsigned long limit = current->signal->rlim[RLIMIT_SWAP].rlim_cur;
+
+ if (limit != RLIM_INFINITY)
+ force_sig(SIGKILL, current);
+}
+
+/*
* We enter with non-exclusive mmap_sem (to exclude vma changes,
* but allow concurrent faults), and pte mapped but not yet locked.
* We return with mmap_sem still held, but pte unmapped and unlocked.
@@ -1667,6 +1679,7 @@ static int do_swap_page(struct mm_struct
entry = pte_to_swp_entry(orig_pte);
page = lookup_swap_cache(entry);
if (!page) {
+ check_swap_rlimit();
swapin_readahead(entry, address, vma);
page = read_swap_cache_async(entry, vma, address);
if (!page) {