Re: [uml-devel] why does index in truncate_inode_pages_range() grows so much ?

[Jan Kara <jack@suse.cz>]

On Fri 13-12-13 14:01:34, Toralf Forster wrote:
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> On 12/13/2013 11:51 AM, Richard Weinberger wrote:
> > On Fri, Dec 13, 2013 at 10:52 AM, Toralf Forster <toralf.foerster@gmx.de> wrote:
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> >> On 12/11/2013 09:26 PM, Jan Kara wrote:
> >>> Thanks! So this works more or less as expected - trinity issued a
> >>> read at absurdly high offset so we created pagecache page a that
> >>> offset and tried to read data into it. That failed. We left the
> >>> page in the pagecache where it was for reclaim to reclaim it when
> >>> free pages are needed. Everything works as designed except we could
> >>> possibly argue that it's not the most efficient way to use
> >>> pages...
> >>>
> >>> Patch 'vfs: fix a bug when we do some dio reads with append dio
> >>> writes' (http://www.spinics.net/lists/linux-fsdevel/msg70899.html)
> >>> should actually change the situation and we won't unnecessarily
> >>> cache these pages.
> >>>
> >> confirmed - applied to latest git tree of Linus I helps.
> > 
> > Good to know! :-)
> > 
> 
> OTOH - there's seems to be more places for an improvement - now trinity
> often runs hours w/o problem (before it runs within a rather short time
> into such issues).
> 
> But today I got another case (I did not patched the source files except
> the mentioned patch by Jan Kara) where the trinity call cycles since 2
> hours w/o any progress. But fortunately the system is still responsive,
> ssh works and I can shutdown that virtual machine smoothly, furthermore
> all local and remote file systems can be unounted cleanly - so that patch
> is a big improvement).
  OK, that is indeed strange. Can you step through find_get_pages() in gdb
to see where exactly are we looping? From the traces below the argument
values look somewhat unreliable so it's not clear to me what is exactly
happening.

								Honza

> tfoerste@n22 ~/devel/github/bingo $ date; sudo gdb /home/tfoerste/devel/linux/linux 9776 -n -batch -ex 'bt'
> Fri Dec 13 13:54:33 CET 2013
> find_get_pages (mapping=0x45182810, start=0, nr_pages=14, pages=0x0) at mm/filemap.c:885
> 885     }
> #0  find_get_pages (mapping=0x45182810, start=0, nr_pages=14, pages=0x0) at mm/filemap.c:885
> #1  0x080d669a in pagevec_lookup (pvec=0x40607d40, mapping=0x0, start=0, nr_pages=0) at mm/swap.c:937
> #2  0x080d6a9a in truncate_inode_pages_range (mapping=0x45182810, lstart=0, lend=-1) at mm/truncate.c:241
> #3  0x080d6e3f in truncate_inode_pages (mapping=0x0, lstart=0) at mm/truncate.c:358
> #4  0x0818c2d2 in ext4_evict_inode (inode=0x45182758) at fs/ext4/inode.c:228
> #5  0x0811b5ff in evict (inode=0x45182758) at fs/inode.c:549
> #6  0x0811c0ed in iput_final (inode=<optimized out>) at fs/inode.c:1419
> #7  iput (inode=0x45182758) at fs/inode.c:1437
> #8  0x08112056 in do_unlinkat (dfd=5, pathname=0x8065d84 <register_lines+276> "") at fs/namei.c:3718
> #9  0x081121c5 in SYSC_unlinkat (flag=<optimized out>, pathname=<optimized out>, dfd=<optimized out>) at fs/namei.c:3754
> #10 SyS_unlinkat (dfd=5, pathname=134634884, flag=0) at fs/namei.c:3746
> #11 0x08062a94 in handle_syscall (r=0x473b59cc) at arch/um/kernel/skas/syscall.c:35
> #12 0x080750f5 in handle_trap (local_using_sysemu=<optimized out>, regs=<optimized out>, pid=<optimized out>) at arch/um/os-Linux/skas/process.c:198
> #13 userspace (regs=0x473b59cc) at arch/um/os-Linux/skas/process.c:431
> #14 0x0805f750 in fork_handler () at arch/um/kernel/process.c:149
> #15 0x5a5a5a5a in ?? ()
> 
> 
> tfoerste@n22 ~/devel/github/bingo $ date; sudo gdb /home/tfoerste/devel/linux/linux 9776 -n -batch -ex 'bt'
> Fri Dec 13 13:54:47 CET 2013
> radix_tree_next_chunk (root=0x3f, iter=0x40607cdc, flags=6) at lib/radix-tree.c:773
> 773                             index &= ~((RADIX_TREE_MAP_SIZE << shift) - 1);
> #0  radix_tree_next_chunk (root=0x3f, iter=0x40607cdc, flags=6) at lib/radix-tree.c:773
> #1  0x080cc88e in find_get_pages (mapping=0x45182810, start=0, nr_pages=14, pages=0x6) at mm/filemap.c:844
> #2  0x080d669a in pagevec_lookup (pvec=0x40607d40, mapping=0x3f, start=63, nr_pages=63) at mm/swap.c:937
> #3  0x080d6a9a in truncate_inode_pages_range (mapping=0x45182810, lstart=0, lend=-1) at mm/truncate.c:241
> #4  0x080d6e3f in truncate_inode_pages (mapping=0x3f, lstart=25769803839) at mm/truncate.c:358
> #5  0x0818c2d2 in ext4_evict_inode (inode=0x45182758) at fs/ext4/inode.c:228
> #6  0x0811b5ff in evict (inode=0x45182758) at fs/inode.c:549
> #7  0x0811c0ed in iput_final (inode=<optimized out>) at fs/inode.c:1419
> #8  iput (inode=0x45182758) at fs/inode.c:1437
> #9  0x08112056 in do_unlinkat (dfd=5, pathname=0x8065d84 <register_lines+276> "") at fs/namei.c:3718
> #10 0x081121c5 in SYSC_unlinkat (flag=<optimized out>, pathname=<optimized out>, dfd=<optimized out>) at fs/namei.c:3754
> #11 SyS_unlinkat (dfd=5, pathname=134634884, flag=0) at fs/namei.c:3746
> #12 0x08062a94 in handle_syscall (r=0x473b59cc) at arch/um/kernel/skas/syscall.c:35
> #13 0x080750f5 in handle_trap (local_using_sysemu=<optimized out>, regs=<optimized out>, pid=<optimized out>) at arch/um/os-Linux/skas/process.c:198
> #14 userspace (regs=0x473b59cc) at arch/um/os-Linux/skas/process.c:431
> #15 0x0805f750 in fork_handler () at arch/um/kernel/process.c:149
> #16 0x5a5a5a5a in ?? ()
> 
> 
> tfoerste@n22 ~/devel/github/bingo $ date; sudo gdb /home/tfoerste/devel/linux/linux 9776 -n -batch -ex 'bt'
> Fri Dec 13 13:57:16 CET 2013
> radix_tree_next_chunk (root=0x10, iter=0x40607cdc, flags=6) at lib/radix-tree.c:769
> 769                                     while (++offset < RADIX_TREE_MAP_SIZE) {
> #0  radix_tree_next_chunk (root=0x10, iter=0x40607cdc, flags=6) at lib/radix-tree.c:769
> #1  0x080cc88e in find_get_pages (mapping=0x45182810, start=0, nr_pages=14, pages=0x6) at mm/filemap.c:844
> #2  0x080d669a in pagevec_lookup (pvec=0x40607d40, mapping=0x10, start=16, nr_pages=16) at mm/swap.c:937
> #3  0x080d6a9a in truncate_inode_pages_range (mapping=0x45182810, lstart=0, lend=-1) at mm/truncate.c:241
> #4  0x080d6e3f in truncate_inode_pages (mapping=0x10, lstart=25769803792) at mm/truncate.c:358
> #5  0x0818c2d2 in ext4_evict_inode (inode=0x45182758) at fs/ext4/inode.c:228
> #6  0x0811b5ff in evict (inode=0x45182758) at fs/inode.c:549
> #7  0x0811c0ed in iput_final (inode=<optimized out>) at fs/inode.c:1419
> #8  iput (inode=0x45182758) at fs/inode.c:1437
> #9  0x08112056 in do_unlinkat (dfd=5, pathname=0x8065d84 <register_lines+276> "") at fs/namei.c:3718
> #10 0x081121c5 in SYSC_unlinkat (flag=<optimized out>, pathname=<optimized out>, dfd=<optimized out>) at fs/namei.c:3754
> #11 SyS_unlinkat (dfd=5, pathname=134634884, flag=0) at fs/namei.c:3746
> #12 0x08062a94 in handle_syscall (r=0x473b59cc) at arch/um/kernel/skas/syscall.c:35
> #13 0x080750f5 in handle_trap (local_using_sysemu=<optimized out>, regs=<optimized out>, pid=<optimized out>) at arch/um/os-Linux/skas/process.c:198
> #14 userspace (regs=0x473b59cc) at arch/um/os-Linux/skas/process.c:431
> #15 0x0805f750 in fork_handler () at arch/um/kernel/process.c:149
> #16 0x5a5a5a5a in ?? ()
> 
> - -- 
> MfG/Sincerely
> Toralf Forster
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-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

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