[Crash-utility] wrong values shown by kmem -s

[vinayak menon]

>
> Something's not adding up, literally, when I compare the old values
> with those shown by your patch.
>
> For examples, without your patch, check just the caches with a single slab page,
> like the nfs_commit_data, fuse_inode and bio-2 caches:
>
>   crash> kmem -s
>   CACHE            NAME                 OBJSIZE  ALLOCATED     TOTAL  SLABS  SSIZE
>   ffff880467c36300 nf_conntrack_ffff880065dd8000 312     0         0      0     8k
>   ffff88046751f900 nf_conntrack_ffff880465411200 312     0         0      0     8k
>   ffff8804608db000 nfs_direct_cache         352          0         0      0     8k
>   ffff8804608daf00 nfs_commit_data          680         23        23      1    16k <=
>   ffff8804608dae00 nfs_read_data            872        447       576     16    32k
>   ffff8804608dad00 nfs_inode_cache         1048       1315      1364     44    32k
>   ffff8804608dac00 fscache_cookie_jar        80        256       276      6     4k
>   ffff88040b958000 fuse_inode               728         21        21      1    16k <=
>   ffff88046751f800 btrfs_delayed_data_ref    96          0         0      0     4k
>   ffff88046751f700 btrfs_delayed_ref_head   160          0         0      0     4k
>   ffff88046751f600 btrfs_delayed_node       304          0         0      0     8k
>   ffff88046751f500 btrfs_ordered_extent     424          0         0      0    16k
>   ffff88046751f400 bio-2                    320         25        25      1     8k <=
>   ...
>
> Taking their respective object sizes into account:
>
>   nfs_commit_data has an object size of 680, and the 16k slab can hold 23 objects:
>     23 * 680 = 15640
>
>   fuse_inode has an object size of 728, and the 16k slab can hold 21 objects:
>     21 * 728 = 15288
>
>   bio-2 has an object size of 320, and the 8k slab can hold 25 objects:
>     25 * 320 = 8000
>
> With your patch applied, note that those caches show double the number above, or
> 46, 42 and 50 respectively:
>
>   crash> kmem -s
>   CACHE            NAME                 OBJSIZE  ALLOCATED     TOTAL  SLABS  SSIZE
>   ffff880467c36300 nf_conntrack_ffff880065dd8000 312     0         0      0     8k
>   ffff88046751f900 nf_conntrack_ffff880465411200 312     0         0      0     8k
>   ffff8804608db000 nfs_direct_cache         352          0         0      0     8k
>   ffff8804608daf00 nfs_commit_data          680         46        46      1    16k
>   ffff8804608dae00 nfs_read_data            872        684       724     15    32k
>   ffff8804608dad00 nfs_inode_cache         1048       1534      1534     43    32k
>   ffff8804608dac00 fscache_cookie_jar        80        532       532      6     4k
>   ffff88040b958000 fuse_inode               728         42        42      1    16k
>   ffff88046751f800 btrfs_delayed_data_ref    96          0         0      0     4k
>   ffff88046751f700 btrfs_delayed_ref_head   160          0         0      0     4k
>   ffff88046751f600 btrfs_delayed_node       304          0         0      0     8k
>   ffff88046751f500 btrfs_ordered_extent     424          0         0      0    16k
>   ffff88046751f400 bio-2                    320         50        50      1     8k
>   ...
>
> What am I missing?
>

Hi Dave,

Looks like this is because of counting the per cpu objects twice. They
are already included in kmem_cache_node.total_objects. This should fix
that. New patch attached.

diff --git a/memory.c b/memory.c
index 7b645b8..1343a11 100644
--- a/memory.c
+++ b/memory.c
@@ -17939,6 +17939,9 @@ get_kmem_cache_slub_data(long cmd, struct meminfo *si)

        total_slabs = total_objects = free_objects = 0;

+       if (VALID_MEMBER(kmem_cache_node_total_objects))
+               node_total_avail = 1;
+
        for (i = 0; i < kt->cpus; i++) {
                cpu_slab_ptr = get_cpu_slab_ptr(si, i, NULL);

@@ -17955,7 +17958,8 @@ get_kmem_cache_slub_data(long cmd, struct meminfo *si)
                            KVADDR, &inuse, sizeof(short),
                            "page inuse", RETURN_ON_ERROR))
                                return FALSE;
-                       total_objects += inuse;
+                       if (!node_total_avail)
+                               total_objects += inuse;
                        total_slabs++;
                        break;

@@ -17992,7 +17996,6 @@ get_kmem_cache_slub_data(long cmd, struct meminfo *si)
                        KVADDR, &node_total_objects, sizeof(ulong),
                        "kmem_cache_node total_objects", RETURN_ON_ERROR))
                                goto bailout;
-                       node_total_avail = 1;
                }

                switch (cmd)
(END)

Vinayak
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