Messages in this thread | | | Date | Sat, 18 Feb 2012 10:35:35 +0400 | From | Konstantin Khlebnikov <> | Subject | Re: [PATCH RFC 00/15] mm: memory book keeping and lru_lock splitting |
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Hugh Dickins wrote: > On Thu, 16 Feb 2012, Hugh Dickins wrote: >> >> Yours are not the only patches I was testing in that tree, I tried to >> gather several other series which I should be reviewing if I ever have >> time: Kamezawa-san's page cgroup diet 6, Xiao Guangrong's 4 prio_tree >> cleanups, your 3 radix_tree changes, your 6 shmem changes, your 4 memcg >> miscellaneous, and then your 15 books. >> >> The tree before your final 15 did well under pressure, until I tried to >> rmdir one of the cgroups afterwards: then it crashed nastily, I'll have >> to bisect into that, probably either Kamezawa's or your memcg changes. > > So far I haven't succeeded in reproducing that at all: it was real, > but obviously harder to get than I assumed - indeed, no good reason > to associate it with any of those patches, might even be in 3.3-rc. > > It did involve a NULL pointer dereference in mem_cgroup_page_lruvec(), > somewhere below compact_zone() - but repercussions were causing the > stacktrace to scroll offscreen, so I didn't get good details.
There some stupid bugs in my v1 patchset, it shouldn't works at all. I did not expect that someone will try to use it. I sent it just to discuss.
Most destructive bug is this PageCgroupUsed() below:
+struct book *page_book(struct page *page) +{ + struct mem_cgroup_per_zone *mz; + struct page_cgroup *pc; + + if (mem_cgroup_disabled()) + return &page_zone(page)->book; + + pc = lookup_page_cgroup(page); + if (!PageCgroupUsed(pc)) + return &page_zone(page)->book; + /* Ensure pc->mem_cgroup is visible after reading PCG_USED. */ + smp_rmb(); + mz = mem_cgroup_zoneinfo(pc->mem_cgroup, + page_to_nid(page), page_zonenum(page)); + return &mz->book; +}
Thus after page uncharge I remove page from wrong book, under wrong lock =)
[ as I wrote, updated patchset there: https://github.com/koct9i/linux ]
> > Hugh
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