On Tue 09-10-12 19:19:09, Hugh Dickins wrote: > On Tue, 9 Oct 2012, Jan Kara wrote: <snip a lot> > > > But here's where I think the problem is. You're assuming that all > > > filesystems go the same mapping_cap_account_writeback_dirty() (yeah, > > > there's no such function, just a confusing maze of three) route as XFS. > > > > > > But filesystems like tmpfs and ramfs (perhaps they're the only two > > > that matter here) don't participate in that, and wait for an mmap'ed > > > page to be seen modified by the user (usually via pte_dirty, but that's > > > a no-op on s390) before page is marked dirty; and page reclaim throws > > > away undirtied pages. > > I admit I haven't thought of tmpfs and similar. After some discussion Mel > > pointed me to the code in mmap which makes a difference. So if I get it > > right, the difference which causes us problems is that on tmpfs we map the > > page writeably even during read-only fault. OK, then if I make the above > > code in page_remove_rmap(): > > if ((PageSwapCache(page) || > > (!anon && !mapping_cap_account_dirty(page->mapping))) && > > page_test_and_clear_dirty(page_to_pfn(page), 1)) > > set_page_dirty(page); > > > > Things should be ok (modulo the ugliness of this condition), right? > > (Setting aside my reservations above...) That's almost exactly right, but > I think the issue of a racing truncation (which could reset page->mapping > to NULL at any moment) means we have to be a bit more careful. Usually > we guard against that with page lock, but here we can rely on mapcount. > > page_mapping(page), with its built-in PageSwapCache check, actually ends > up making the condition look less ugly; and so far as I could tell, > the extra code does get optimized out on x86 (unless CONFIG_DEBUG_VM, > when we are left with its VM_BUG_ON(PageSlab(page))). > > But please look this over very critically and test (and if you like it, > please adopt it as your own): I'm not entirely convinced yet myself. Just to followup on this. The new version of the patch runs fine for several days on our s390 build machines. I was also running fsx-linux on tmpfs while pushing the machine to swap. fsx ran fine but I hit WARN_ON(delalloc) in xfs_vm_releasepage(). The exact stack trace is: [<000003c008edb38e>] xfs_vm_releasepage+0xc6/0xd4 [xfs] [<0000000000213326>] shrink_page_list+0x6ba/0x734 [<0000000000213924>] shrink_inactive_list+0x230/0x578 [<0000000000214148>] shrink_list+0x6c/0x120 [<00000000002143ee>] shrink_zone+0x1f2/0x238 [<0000000000215482>] balance_pgdat+0x5f6/0x86c [<00000000002158b8>] kswapd+0x1c0/0x248 [<000000000017642a>] kthread+0xa6/0xb0 [<00000000004e58be>] kernel_thread_starter+0x6/0xc [<00000000004e58b8>] kernel_thread_starter+0x0/0xc I don't think it is really related but I'll hold off the patch for a while to investigate what's going on... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>