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    SubjectRe: [RFC PATCH 5/5] mm, memory_hotplug: be more verbose for memory offline failures
    On Wed,  7 Nov 2018 11:18:30 +0100 Michal Hocko <mhocko@kernel.org> wrote:

    > From: Michal Hocko <mhocko@suse.com>
    >
    > There is only very limited information printed when the memory offlining
    > fails:
    > [ 1984.506184] rac1 kernel: memory offlining [mem 0x82600000000-0x8267fffffff] failed due to signal backoff
    >
    > This tells us that the failure is triggered by the userspace
    > intervention but it doesn't tell us much more about the underlying
    > reason. It might be that the page migration failes repeatedly and the
    > userspace timeout expires and send a signal or it might be some of the
    > earlier steps (isolation, memory notifier) takes too long.
    >
    > If the migration failes then it would be really helpful to see which
    > page that and its state. The same applies to the isolation phase. If we
    > fail to isolate a page from the allocator then knowing the state of the
    > page would be helpful as well.
    >
    > Dump the page state that fails to get isolated or migrated. This will
    > tell us more about the failure and what to focus on during debugging.
    >
    > ...
    >
    > --- a/mm/memory_hotplug.c
    > +++ b/mm/memory_hotplug.c
    > @@ -1388,10 +1388,8 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
    > page_is_file_cache(page));
    >
    > } else {
    > -#ifdef CONFIG_DEBUG_VM
    > - pr_alert("failed to isolate pfn %lx\n", pfn);
    > + pr_warn("failed to isolate pfn %lx\n", pfn);
    > dump_page(page, "isolation failed");
    > -#endif
    > put_page(page);
    > /* Because we don't have big zone->lock. we should
    > check this again here. */
    > @@ -1411,8 +1409,14 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
    > /* Allocate a new page from the nearest neighbor node */
    > ret = migrate_pages(&source, new_node_page, NULL, 0,
    > MIGRATE_SYNC, MR_MEMORY_HOTPLUG);
    > - if (ret)
    > + if (ret) {
    > + list_for_each_entry(page, &source, lru) {
    > + pr_warn("migrating pfn %lx failed ",
    > + page_to_pfn(page), ret);
    > + dump_page(page, NULL);
    > + }

    ./include/linux/kern_levels.h:5:18: warning: too many arguments for format [-Wformat-extra-args]
    #define KERN_SOH "\001" /* ASCII Start Of Header */
    ^
    ./include/linux/kern_levels.h:12:22: note: in expansion of macro ‘KERN_SOH’
    #define KERN_WARNING KERN_SOH "4" /* warning conditions */
    ^~~~~~~~
    ./include/linux/printk.h:310:9: note: in expansion of macro ‘KERN_WARNING’
    printk(KERN_WARNING pr_fmt(fmt), ##__VA_ARGS__)
    ^~~~~~~~~~~~
    ./include/linux/printk.h:311:17: note: in expansion of macro ‘pr_warning’
    #define pr_warn pr_warning
    ^~~~~~~~~~
    mm/memory_hotplug.c:1414:5: note: in expansion of macro ‘pr_warn’
    pr_warn("migrating pfn %lx failed ",
    ^~~~~~~

    --- a/mm/memory_hotplug.c~mm-memory_hotplug-be-more-verbose-for-memory-offline-failures-fix
    +++ a/mm/memory_hotplug.c
    @@ -1411,7 +1411,7 @@ do_migrate_range(unsigned long start_pfn
    MIGRATE_SYNC, MR_MEMORY_HOTPLUG);
    if (ret) {
    list_for_each_entry(page, &source, lru) {
    - pr_warn("migrating pfn %lx failed ",
    + pr_warn("migrating pfn %lx failed: %d",
    page_to_pfn(page), ret);
    dump_page(page, NULL);
    }
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