Messages in this thread | | | Date | Thu, 22 Jul 2021 13:29:23 +0100 | From | Matthew Wilcox <> | Subject | Re: [PATCH v14 062/138] mm/migrate: Add folio_migrate_copy() |
| |
On Thu, Jul 22, 2021 at 02:52:28PM +0300, Dmitry Osipenko wrote: > I'm getting warnings that might be related to this patch.
Thank you! This is a good report. I've trimmed away some of the unnecessary bits from below:
> BUG: sleeping function called from invalid context at mm/util.c:761 > in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 29, name: kcompactd0
This is absolutely a result of this patch:
for (i = 0; i < nr; i++) { cond_resched(); copy_highpage(folio_page(dst, i), folio_page(src, i)); }
cond_resched() can sleep, of course. This is new; previously only copying huge pages would call cond_resched(). Now every page copy calls cond_resched().
> (___might_sleep) from (folio_copy+0x3f/0x84) > (folio_copy) from (folio_migrate_copy+0x11/0x1c) > (folio_migrate_copy) from (__buffer_migrate_page.part.0+0x215/0x238) > (__buffer_migrate_page.part.0) from (buffer_migrate_page_norefs+0x19/0x28)
__buffer_migrate_page() is where we become atomic:
if (check_refs) spin_lock(&mapping->private_lock); ... migrate_page_copy(newpage, page); ... if (check_refs) spin_unlock(&mapping->private_lock);
> (buffer_migrate_page_norefs) from (move_to_new_page+0x4d/0x200) > (move_to_new_page) from (migrate_pages+0x521/0x72c) > (migrate_pages) from (compact_zone+0x589/0xb60)
The obvious solution is just to change folio_copy():
{ - unsigned i, nr = folio_nr_pages(src); + unsigned i = 0; + unsigned nr = folio_nr_pages(src);
- for (i = 0; i < nr; i++) { - cond_resched(); + for (;;) { copy_highpage(folio_page(dst, i), folio_page(src, i)); + if (i++ == nr) + break; + cond_resched(); } }
now it only calls cond_resched() for multi-page folios.
But that leaves us with a bit of an ... impediment to using multi-page folios for buffer-head based filesystems (and block devices). I must admit to not knowing the buffer_head locking scheme quite as well as I would like to. Is it possible to drop this spinlock earlier?
| |