Dne 27.11.2012 21:58, Linus Torvalds napsal(a):
Note that in the meantime, I've also applied (through Andrew) the patch that reverts commit c654345924f7 (see commit 82b212f40059 'Revert "mm: remove __GFP_NO_KSWAPD"'). I wonder if that revert may be bogus, and a result of this same issue. Maybe that revert should be reverted, and replaced with your patch? Mel? Zdenek? What's the status here?
I've tried for longer term: https://lkml.org/lkml/2012/11/5/308 https://lkml.org/lkml/2012/11/12/113 these 2 seems to be now merge in -rc7 (since they disappeared after my git rebase) and added slightly modified patch from Jiri (https://lkml.org/lkml/2012/11/15/950 (Unsure where it still applies for -rc7??) Also I've Jan Kara <jack@xxxxxxx> fs: Fix imbalance in freeze protection in mark_files_ro() (which is still not applied to upstream) And I think I'm NOT seeing huge load from kswapd0. (At least related to my not really long uptimes) But also I'm now frequent victim of my other report: https://lkml.org/lkml/2012/11/15/369 Which turns into a problem, that if my T61 docking station has enabled support for 'old hw' for docking in BIOS - i.e. serial output' it becomes unstable and either 1st. or 2nd. resume deadlocks machine - and serial port gives just garbage) Zdenek
Linus On Tue, Nov 27, 2012 at 12:48 PM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote:Hi everyone, I hope I included everybody that participated in the various threads on kswapd getting stuck / exhibiting high CPU usage. We were looking at at least three root causes as far as I can see, so it's not really clear who observed which problem. Please correct me if the reported-by, tested-by, bisected-by tags are incomplete. One problem was, as it seems, overly aggressive reclaim due to scaling up reclaim goals based on compaction failures. This one was reverted in 9671009 mm: revert "mm: vmscan: scale number of pages reclaimed by reclaim/compaction based on failures". Another one was an accounting problem where a freed higher order page was underreported, and so kswapd had trouble restoring watermarks. This one was fixed in ef6c5be fix incorrect NR_FREE_PAGES accounting (appears like memory leak). The third one is a problem with small zones, like the DMA zone, where the high watermark is lower than the low watermark plus compaction gap (2 * allocation size). The zonelist reclaim in kswapd would do nothing because all high watermarks are met, but the compaction logic would find its own requirements unmet and loop over the zones again. Indefinitely, until some third party would free enough memory to help meet the higher compaction watermark. The problematic code has been there since the 3.4 merge window for non-THP higher order allocations but has been more prominent since the 3.7 merge window, where kswapd is also woken up for the much more common THP allocations. The following patch should fix the third issue by making both reclaim and compaction code in kswapd use the same predicate to determine whether a zone is balanced or not. Hopefully, the sum of all three fixes should tame kswapd enough for 3.7. Johannes
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