Messages in this thread | | | Date | Tue, 20 Nov 2012 18:43:04 +0100 | From | Thorsten Leemhuis <> | Subject | Re: [PATCH] Revert "mm: remove __GFP_NO_KSWAPD" |
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On 20.11.2012 16:38, Josh Boyer wrote: > On Fri, Nov 16, 2012 at 3:06 PM, Mel Gorman <mgorman@suse.de> wrote: >> On Fri, Nov 16, 2012 at 02:14:47PM -0500, Josh Boyer wrote: >>> On Mon, Nov 12, 2012 at 6:37 AM, Mel Gorman <mgorman@suse.de> wrote: >>>> With "mm: vmscan: scale number of pages reclaimed by reclaim/compaction >>>> based on failures" reverted, Zdenek Kabelac reported the following >>>> >>>> Hmm, so it's just took longer to hit the problem and observe >>>> kswapd0 spinning on my CPU again - it's not as endless like before - >>>> but still it easily eats minutes - it helps to turn off Firefox >>>> or TB (memory hungry apps) so kswapd0 stops soon - and restart >>>> those apps again. (And I still have like >1GB of cached memory) >>>> >>>> kswapd0 R running task 0 30 2 0x00000000 >>>> ffff8801331efae8 0000000000000082 0000000000000018 0000000000000246 >>>> ffff880135b9a340 ffff8801331effd8 ffff8801331effd8 ffff8801331effd8 >>>> ffff880055dfa340 ffff880135b9a340 00000000331efad8 ffff8801331ee000 >>>> Call Trace: >>>> [<ffffffff81555bf2>] preempt_schedule+0x42/0x60 >>>> [<ffffffff81557a95>] _raw_spin_unlock+0x55/0x60 >>>> [<ffffffff81192971>] put_super+0x31/0x40 >>>> [<ffffffff81192a42>] drop_super+0x22/0x30 >>>> [<ffffffff81193b89>] prune_super+0x149/0x1b0 >>>> [<ffffffff81141e2a>] shrink_slab+0xba/0x510 >>>> >>>> The sysrq+m indicates the system has no swap so it'll never reclaim >>>> anonymous pages as part of reclaim/compaction. That is one part of the >>>> problem but not the root cause as file-backed pages could also be reclaimed. >>>> >>>> The likely underlying problem is that kswapd is woken up or kept awake >>>> for each THP allocation request in the page allocator slow path. >>>> >>>> If compaction fails for the requesting process then compaction will be >>>> deferred for a time and direct reclaim is avoided. However, if there >>>> are a storm of THP requests that are simply rejected, it will still >>>> be the the case that kswapd is awake for a prolonged period of time >>>> as pgdat->kswapd_max_order is updated each time. This is noticed by >>>> the main kswapd() loop and it will not call kswapd_try_to_sleep(). >>>> Instead it will loopp, shrinking a small number of pages and calling >>>> shrink_slab() on each iteration. >>>> >>>> The temptation is to supply a patch that checks if kswapd was woken for >>>> THP and if so ignore pgdat->kswapd_max_order but it'll be a hack and not >>>> backed up by proper testing. As 3.7 is very close to release and this is >>>> not a bug we should release with, a safer path is to revert "mm: remove >>>> __GFP_NO_KSWAPD" for now and revisit it with the view to ironing out the >>>> balance_pgdat() logic in general. >>>> >>>> Signed-off-by: Mel Gorman <mgorman@suse.de> >>> >>> Does anyone know if this is queued to go into 3.7 somewhere? I looked >>> a bit and can't find it in a tree. We have a few reports of Fedora >>> rawhide users hitting this. >> >> No, because I was waiting to hear if a) it worked and preferably if the >> alternative "less safe" option worked. This close to release it might be >> better to just go with the safe option. > > We've been tracking it in https://bugzilla.redhat.com/show_bug.cgi?id=866988 > and people say this revert patch doesn't seem to make the issue go away > fully. Thorsten has created another kernel with the other patch applied > for testing. > > At least I think that is the latest status from the bug. Hopefully the > commenters will chime in.
The short story from my current point of view is:
* my main machine at home where I initially saw the issue that started this thread seems to be running fine with rc6 and the "safe" patch Mel posted in https://lkml.org/lkml/2012/11/12/113 Before that I ran a rc5 kernel with the revert that went into rc6 and the "safe" patch -- that worked fine for a few days, too.
* I have a second machine where I started to use 3.7-rc kernels only yesterday (the machine triggered a bug in the radeon driver that seems to be fixed in rc6) which showed symptoms like the ones Zdenek Kabelac mentions in this thread. I wasn't able to look closer at it, but simply tried rc6 with the safe patch, which didn't help. I'm now running rc6 with the "riskier" patch from https://lkml.org/lkml/2012/11/12/151 I can't yet tell if it helps. If the problems shows up again I'll try to capture more debugging data via sysrq -- there wasn't any time for that when I was running rc6 with the safe patch, sorry.
Thorsten
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