#21705: Segmentation Faults when using Swap on ar71xx (zram)
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Reporter: mt@… | Owner: developers
Type: defect | Status: new
Priority: normal | Milestone:
Component: kernel | Version: Chaos Calmer 15.05
Resolution: | Keywords: swap,zram
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Comment (by mt@…):
@diizzyy
It's 32mb memory - usable are around 28mb and zram by default uses 14mb
for swap. This usally compresses to 1/3 so at most 4-5mb memory should be
used by zram.
I've thought this and experimented with limited the amount zram can use:
there is
/sys/block/zram0/limit but it had no effect
And I've reduced zram usage to 10 and 4mb for the swap device.
/proc/meminfo says 8mb are free and having only 4mb zram would use no more
than 1-2mb memory.
However independent of the amount of swap or zram I've see the crashes.
This also happyens when just using luci and low memory pressure albeit not
as often.
I suspect it's some bug related to swap and not directly related to zram.
I've filled a 5mb zram device sucessfully with /dev/urandom and reading
that back works fine.
The crashes are happening on do_page_fault in the kernel, so swapped out
pages are accessed and something seems to wrong.
There seems to be issues - here is an unmerged patch that mentions crashes
when using swap: http://patchwork.linux-mips.org/patch/7615/
I'm not a kernel dev by any means and applying the patch series did not
work out of the box so I'm not sure if that's related.
--
Ticket URL: <https://dev.openwrt.org/ticket/21705#comment:3>
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