Hi Michal,
I'm over a very long kernel bisection, and if I made no mistake in
testing commits, this patch fixes a kernel bug which affects my HP
Compaq dc5800 machine with 32 bit Ubuntu OS.
The bug manifests itself with "NMI watchdog: BUG: soft lockup - CPU#0
stuck for 23s! [kswapd0:38]" messages in 4.8 kernels, and "page
allocation stalls for 47608ms, order:1,
mode:0x17000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK)" in 4.10 kernels up
to this commit.
Michal, can you confirm that this patch may fix issues like the ones I
encountered? If so, I'll try to get the Ubuntu kernel staff to
backport this commit to Yakkety's 4.8 kernel. On the other hand, I
can't seem to be able to backport this commit to 4.8 with "git
cherry-pick", so maybe I need to wait for your tweaks you mentioned.
Anyway, thank you very much for the fix!
Regards,
MegaBrutal
2017-02-28 16:11 GMT+01:00 Michal Hocko <[email protected]>:
>
> From: Michal Hocko <[email protected]>
>
> commit 71ab6cfe88dcf9f6e6a65eb85cf2bda20a257682 upstream.
>
> get_scan_count() considers the whole node LRU size when
>
> - doing SCAN_FILE due to many page cache inactive pages
> - calculating the number of pages to scan
>
> In both cases this might lead to unexpected behavior especially on 32b
> systems where we can expect lowmem memory pressure very often.
>
> A large highmem zone can easily distort SCAN_FILE heuristic because
> there might be only few file pages from the eligible zones on the node
> lru and we would still enforce file lru scanning which can lead to
> trashing while we could still scan anonymous pages.
>
> The later use of lruvec_lru_size can be problematic as well. Especially
> when there are not many pages from the eligible zones. We would have to
> skip over many pages to find anything to reclaim but shrink_node_memcg
> would only reduce the remaining number to scan by SWAP_CLUSTER_MAX at
> maximum. Therefore we can end up going over a large LRU many times
> without actually having chance to reclaim much if anything at all. The
> closer we are out of memory on lowmem zone the worse the problem will
> be.
>
> Fix this by filtering out all the ineligible zones when calculating the
> lru size for both paths and consider only sc->reclaim_idx zones.
>
> The patch would need to be tweaked a bit to apply to 4.10 and older but
> I will do that as soon as it hits the Linus tree in the next merge
> window.
>
> Link: http://lkml.kernel.org/r/[email protected]
> Fixes: b2e18757f2c9 ("mm, vmscan: begin reclaiming pages on a per-node basis")
> Signed-off-by: Michal Hocko <[email protected]>
> Tested-by: Trevor Cordes <[email protected]>
> Acked-by: Minchan Kim <[email protected]>
> Acked-by: Hillf Danton <[email protected]>
> Acked-by: Mel Gorman <[email protected]>
> Acked-by: Johannes Weiner <[email protected]>
> Cc: <[email protected]> [4.8+]
> Signed-off-by: Andrew Morton <[email protected]>
> Signed-off-by: Linus Torvalds <[email protected]>
> ---
> mm/vmscan.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index cd516c632e8f..30a88b945a44 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2205,7 +2205,7 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
> * system is under heavy pressure.
> */
> if (!inactive_list_is_low(lruvec, true, sc) &&
> - lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, MAX_NR_ZONES) >> sc->priority) {
> + lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, sc->reclaim_idx) >> sc->priority) {
> scan_balance = SCAN_FILE;
> goto out;
> }
> @@ -2272,7 +2272,7 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
> unsigned long size;
> unsigned long scan;
>
> - size = lruvec_lru_size(lruvec, lru, MAX_NR_ZONES);
> + size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
> scan = size >> sc->priority;
>
> if (!scan && pass && force_scan)
> --
> 2.11.0
>
On Mon 06-03-17 19:00:00, MegaBrutal wrote:
> Hi Michal,
>
> I'm over a very long kernel bisection, and if I made no mistake in
> testing commits, this patch fixes a kernel bug which affects my HP
> Compaq dc5800 machine with 32 bit Ubuntu OS.
>
> The bug manifests itself with "NMI watchdog: BUG: soft lockup - CPU#0
> stuck for 23s! [kswapd0:38]" messages in 4.8 kernels, and "page
> allocation stalls for 47608ms, order:1,
> mode:0x17000c0(GFP_KERNEL_ACCOUNT|__GFP_NOTRACK)" in 4.10 kernels up
> to this commit.
This is really hard to say without seeing the traces.
> Michal, can you confirm that this patch may fix issues like the ones I
> encountered? If so, I'll try to get the Ubuntu kernel staff to
> backport this commit to Yakkety's 4.8 kernel. On the other hand, I
> can't seem to be able to backport this commit to 4.8 with "git
> cherry-pick", so maybe I need to wait for your tweaks you mentioned.
The backport from 4.9 to 4.8 shouldn't be very complicated I believe.
> Anyway, thank you very much for the fix!
Good to hear the patch helped you though.
--
Michal Hocko
SUSE Labs