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    SubjectRe: Memory corruption during hibernation since 2.6.31
    Hi everyone,

    On Thu, Jul 29, 2010 at 11:44:31AM -0700, Hugh Dickins wrote:
    > I've CC'ed Andrea because we were having an offline conversation about
    > whether ksmd (and his khugepaged) need to set_freezable(); and I wonder
    > if this swap bug underlies his interest, though he was mainly worrying
    > about I/O in progress.

    My opinion is that with current freezer model it is needed for suspend
    to disk. The kthread_should_stop seems useless for kswapd/ksmd, but
    I'm afraid it might get useful in the future so just to stay on the
    safe side I added it to khugepaged as well, but it's contributing to
    the pollution.

    I've no idea why the freezing isn't preemptive (through the scheduler,
    all these kernel threads are obviously lowlatency beasts) by default
    (if kthread doesn't run set_freezable) and instead it requires
    cooperative freezing. Now I can imagine a kernel thread not being
    happy about preemptive freezing, and I also can imagine a kernel
    thread not being happy about being frozen. But I think the default
    shall be "preempting freezing by default" (removing all those
    set_freezable/try_to_freeze and furthermore reducing the latency it
    takes to freeze the task without having to add !freezing(current)
    checks in the loops, by taking advantage of the existing cond_resched
    or preempt=Y) and then introduce a set_freezable_cooperative() if it
    wants to call try_to_freeze in a cooperative way in a well defined
    point of the code, or set_not_freezable() if it doesn't want to
    be frozen.

    But for now I'm afraid the below is needed (only ksm.c part applies to

    Subject: freeze khugepaged and ksmd

    From: Andrea Arcangeli <>

    It's unclear why schedule friendly kernel threads can't be taken away by the
    CPU through the scheduler itself. It's safer to stop them as they can trigger
    memory allocation, if kswapd also freezes itself to avoid generating I/O they
    have too.

    Signed-off-by: Andrea Arcangeli <>

    diff --git a/mm/huge_memory.c b/mm/huge_memory.c
    --- a/mm/huge_memory.c
    +++ b/mm/huge_memory.c
    @@ -15,6 +15,7 @@
    #include <linux/mm_inline.h>
    #include <linux/kthread.h>
    #include <linux/khugepaged.h>
    +#include <linux/freezer.h>
    #include <asm/tlb.h>
    #include <asm/pgalloc.h>
    #include "internal.h"
    @@ -2053,6 +2054,9 @@ static void khugepaged_do_scan(struct pa

    + if (unlikely(kthread_should_stop() || freezing(current)))
    + break;
    if (!khugepaged_scan.mm_slot)
    @@ -2115,6 +2119,9 @@ static void khugepaged_loop(void)
    if (hpage)
    + try_to_freeze();
    + if (unlikely(kthread_should_stop()))
    + break;
    if (khugepaged_has_work()) {
    if (!khugepaged_scan_sleep_millisecs)
    @@ -2134,6 +2141,7 @@ static int khugepaged(void *none)
    struct mm_slot *mm_slot;

    + set_freezable();
    set_user_nice(current, 19);

    /* serialize with start_khugepaged() */
    @@ -2148,6 +2156,8 @@ static int khugepaged(void *none)
    if (!khugepaged_enabled())
    + if (unlikely(kthread_should_stop()))
    + break;

    diff --git a/mm/ksm.c b/mm/ksm.c
    --- a/mm/ksm.c
    +++ b/mm/ksm.c
    @@ -33,6 +33,7 @@
    #include <linux/mmu_notifier.h>
    #include <linux/swap.h>
    #include <linux/ksm.h>
    +#include <linux/freezer.h>

    #include <asm/tlbflush.h>
    #include "internal.h"
    @@ -1386,7 +1387,7 @@ static void ksm_do_scan(unsigned int sca
    struct rmap_item *rmap_item;
    struct page *uninitialized_var(page);

    - while (scan_npages--) {
    + while (scan_npages-- && likely(!freezing(current))) {
    rmap_item = scan_get_next_rmap_item(&page);
    if (!rmap_item)
    @@ -1412,6 +1413,8 @@ static int ksm_scan_thread(void *nothing

    + try_to_freeze();
    if (ksmd_should_run()) {
    @@ -1953,6 +1956,7 @@ static int __init ksm_init(void)
    struct task_struct *ksm_thread;
    int err;

    + set_freezable();
    err = ksm_slab_init();
    if (err)
    goto out;

     \ /
      Last update: 2010-07-29 20:59    [W:0.161 / U:1.272 seconds]
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