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    SubjectRe: 2.6.26-rc5-mm2
    Date
    On Tuesday 10 June 2008 18:34, Andrew Morton wrote:
    > On Tue, 10 Jun 2008 17:28:27 +1000 Nick Piggin <nickpiggin@yahoo.com.au>
    wrote:
    > > On Tuesday 10 June 2008 15:31, Andrew Morton wrote:
    > > > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.26-rc
    > > >5/2. 6.26-rc5-mm2/
    > >
    > > BTW. would be trying to test this more myself, but last mm I based the
    > > lockless patches on didn't boot, and this one dies pretty quickly when
    > > you try to get into reclaim:
    > >
    > > ------------[ cut here ]------------
    > > kernel BUG at mm/swap_state.c:77!
    > > invalid opcode: 0000 [1] SMP DEBUG_PAGEALLOC
    > > last sysfs file: /sys/devices/system/cpu/cpu7/cache/index2/shared_cpu_map
    > > CPU 7
    > > Modules linked in:
    > > Pid: 13550, comm: sh Not tainted 2.6.26-rc5-mm2-dirty #412
    > > RIP: 0010:[<ffffffff80288689>] [<ffffffff80288689>]
    > > add_to_swap_cache+0xd9/0x120
    > > RSP: 0018:ffff81010c62d8a8 EFLAGS: 00010246
    > > RAX: 2000000000020009 RBX: ffffe2000107da88 RCX: c000000000000000
    > > RDX: 0000000000000020 RSI: 000000000000eea2 RDI: ffffe2000107da88
    > > RBP: ffff81010c62d8c8 R08: fffffffffa48016e R09: 0000000000000000
    > > R10: ffffffff80857fa0 R11: 2222222222222222 R12: ffff81012e126520
    > > R13: 000000000000eea2 R14: ffff8100727bea20 R15: ffff81010c62d9b8
    > > FS: 00002b5b33cafdc0(0000) GS:ffff81012ff07800(0000)
    > > knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
    > > CR2: 000000000175e280 CR3: 000000012e292000 CR4: 00000000000006e0
    > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    > > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
    > > Process sh (pid: 13550, threadinfo ffff81010c62c000, task
    > > ffff810116b01110) Stack: ffff81010c62d8c8 ffffe2000107da88
    > > ffff81012e126520 ffff81012e126400 ffff81010c62d908 ffffffff80292851
    > > 000000000000eea2 ffff81012e126708 ffffe2000107da88 ffffffff80701420
    > > ffff81010c62db68 ffff81010c62dc88 Call Trace:
    > > [<ffffffff80292851>] shmem_writepage+0x121/0x200
    > > [<ffffffff80277479>] shrink_page_list+0x559/0x6b0
    > > [<ffffffff802777ec>] shrink_list+0x21c/0x520
    > > [<ffffffff80273365>] ? determine_dirtyable_memory+0x15/0x30
    > > [<ffffffff802733a2>] ? get_dirty_limits+0x22/0x2a0
    > > [<ffffffff80277d31>] shrink_zone+0x241/0x330
    > > [<ffffffff80278207>] try_to_free_pages+0x237/0x3a0
    > > [<ffffffff80276530>] ? isolate_pages_global+0x0/0x270
    > > [<ffffffff80272546>] __alloc_pages_internal+0x206/0x4b0
    > > [<ffffffff8028dfd7>] alloc_pages_current+0x87/0xd0
    > > [<ffffffff802714fe>] __get_free_pages+0xe/0x60
    > > [<ffffffff802343ca>] copy_process+0xba/0x1240
    > > [<ffffffff80235682>] do_fork+0x82/0x2a0
    > > [<ffffffff8025a03d>] ? trace_hardirqs_on+0xd/0x10
    > > [<ffffffff805177ab>] ? _spin_unlock_irq+0x2b/0x40
    > > [<ffffffff8051703f>] ? trace_hardirqs_on_thunk+0x3a/0x3f
    > > [<ffffffff8020b6cb>] ? system_call_after_swapgs+0x7b/0x80
    > > [<ffffffff80209853>] sys_clone+0x23/0x30
    > >
    > > The tmpfs PageSwapBacked stuff seems rather broken. For
    > > them write_begin/write_end path, it is filemap.c, not shmem.c,
    > > which allocates the page, so its no wonder it goes bug. Will
    > > try to do more testing without shmem.
    >
    > rikstuff. Could be that the merge caused a problem?

    Doesn't look like it, but I hadn't followed the changes too closely:
    rather they just need to test loopback over tmpfs.


    > > Also, just noticed
    > > mm/memory.c:do_wp_page
    > > //TODO: is this safe? do_anonymous_page() does it this way.
    > >
    > > That's a bit disheartening. Surely a question like that has to
    > > be answered definitively?
    >
    > I asked that too.
    >
    > > (hopefully whatever is doing the
    > > asking won't get merged until answered)
    >
    > It would be good if you could find a day to look through those changes
    > please. It's pretty important.

    OK, I could have a look through them at some point.

    Just something very quick while I have Rik's attention are all the
    atomic SetPageSwapBacked bitops over a lot of mm/ fastpaths that I have
    been slowly working away to get rid of over the past years. Maybe some
    don't consider it a big deal, but a single one costs anywhere from
    100 - 500 instructions on desktop CPUs, not including secondary effects
    of ordering memory and and compiler barrier. Please go through and
    ensure you know your page references and ->flags concurrency, and cut
    these down to a bare minimum.

    Is the plan to merge all reclaim changes in a big hit, rather than
    slowly trickle in the different independent changes?


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