[Crash-utility] Re: [PATCH] memory: handle kmem_cache per-node pointer layout

Hi Harshvardhan, On Mon, Aug 17, 2026 at 12: 02 AM Harshvardhan Jha <harshvardhan. j. jha(a) oracle. com&gt; wrote: > > Linux commit 5ba6bc27b1f9 ("slab: decouple pointer to barn from > kmem_cache_node") moved the kmem_cache_node pointers Hi Harshvardhan, On Mon, Aug 17, 2026 at 12:02 AM Harshvardhan Jha <harshvardhan.j.jha(a)oracle.com&gt; wrote: > > Linux commit 5ba6bc27b1f9 ("slab: decouple pointer to barn from > kmem_cache_node") moved the kmem_cache_node pointers from > kmem_cache.node[] to kmem_cache.per_node[].node. > > Teach the SLUB traversal code to recognize and handle both layouts. > Without this, crash treats the new layout as non-NUMA and kmem -s fails > while looking for the removed kmem_cache.local_node member. > > Signed-off-by: Harshvardhan Jha <harshvardhan.j.jha(a)oracle.com&gt; > --- > Testing was performed manually on x86_64 VMs: > > - Linux 7.1.0-rc7 with the new per_node layout: upstream crash failed > with the kmem_cache_local_node invalid-offset error, while the patched > crash completed kmem -s and displayed the slab-cache table. > - Linux 6.18.0-rc7 with the old node[1024] layout: the patched crash > completed kmem -s and displayed the slab-cache table. > > defs.h | 3 +++ > memory.c | 39 ++++++++++++++++++++++++++++++--------- > symbols.c | 6 ++++++ > 3 files changed, 39 insertions(+), 9 deletions(-) > > diff --git a/defs.h b/defs.h > index e3027e2..ccd84a0 100644 > --- a/defs.h > +++ b/defs.h > @@ -1766,6 +1766,8 @@ struct offset_table { /* stash of commonly-used offsets */ > long kmem_cache_name; > long kmem_cache_list; > long kmem_cache_node; > + long kmem_cache_per_node; > + long kmem_cache_per_node_node; > long kmem_cache_cpu_slab; > long page_inuse; > /* long page_offset; use "old" page->offset */ > @@ -2395,6 +2397,7 @@ struct size_table { /* stash of commonly-used sizes */ > long rlimit; > long kmem_cache; > long kmem_cache_node; > + long kmem_cache_per_node_ptrs; The offset_table & size_table, any new added members should be appended at the end of the struct, not in the middle. Please check https://urldefense.com/v3/__https://github.com/crash-utility/crash/ wiki*writing-patches__;Iw!!ACWV5N9M2RV99hQ! O1Hf-3Yy5Z2kcbB75VvSaoFma69uN3QLn5J1UKeIbTvRAvowZJrHLu3BkU7jc4hhXGWmI3MhLcfPYQC29tY$ <https://urldefense.com/v3/__https://github.com/crash-utility/crash/wiki*w... > long upid; > long kmem_cache_cpu; > long cfs_rq; > diff --git a/memory.c b/memory.c > index 3f3aa27..cf26bd4 100644 > --- a/memory.c > +++ b/memory.c > @@ -306,6 +306,7 @@ static int get_kmem_cache_list(ulong **); > static int get_kmem_cache_root_list(ulong **); > static int get_kmem_cache_child_list(ulong **, ulong); > static int get_kmem_cache_slub_data(long, struct meminfo *); > +static ulong get_kmem_cache_node_ptr(struct meminfo *, int); > static ulong compound_head(ulong); > static long count_partial(ulong, struct meminfo *, ulong *); > static short count_cpu_partial(struct meminfo *, int); > @@ -869,6 +870,9 @@ vm_init(void) > MEMBER_OFFSET_INIT(kmem_cache_inuse, "kmem_cache", "inuse"); > MEMBER_OFFSET_INIT(kmem_cache_align, "kmem_cache", "align"); > MEMBER_OFFSET_INIT(kmem_cache_node, "kmem_cache", "node"); > + MEMBER_OFFSET_INIT(kmem_cache_per_node, "kmem_cache", "per_node"); > + MEMBER_OFFSET_INIT(kmem_cache_per_node_node, > + "kmem_cache_per_node_ptrs", "node"); > MEMBER_OFFSET_INIT(kmem_cache_cpu_slab, "kmem_cache", "cpu_slab"); > MEMBER_OFFSET_INIT(kmem_cache_list, "kmem_cache", "list"); > MEMBER_OFFSET_INIT(kmem_cache_red_left_pad, "kmem_cache", "red_left_pad"); > @@ -920,9 +924,16 @@ vm_init(void) > if (INVALID_MEMBER(page_objects)) > ANON_MEMBER_OFFSET_INIT(page_objects, "slab", "objects"); > } > + STRUCT_SIZE_INIT(kmem_cache_per_node_ptrs, > + "kmem_cache_per_node_ptrs"); > if (VALID_MEMBER(kmem_cache_node)) { > ARRAY_LENGTH_INIT(len, NULL, "kmem_cache.node", NULL, 0); > vt->flags |= CONFIG_NUMA; > + } else if (VALID_MEMBER(kmem_cache_per_node) && > + VALID_MEMBER(kmem_cache_per_node_node) && > + VALID_SIZE(kmem_cache_per_node_ptrs)) { > + ARRAY_LENGTH_INIT(len, NULL, "kmem_cache.per_node", NULL, 0); > + vt->flags |= CONFIG_NUMA; > } > ARRAY_LENGTH_INIT(len, NULL, "kmem_cache.cpu_slab", NULL, 0); > > @@ -19460,6 +19471,22 @@ count_cpu_partial(struct meminfo *si, int cpu) > return free_objects; > } > > +static ulong > +get_kmem_cache_node_ptr(struct meminfo *si, int node) > +{ > + char *node_addr; > + > + if (VALID_MEMBER(kmem_cache_node)) > + node_addr = si->cache_buf + OFFSET(kmem_cache_node) + > + (sizeof(void *) * node); > + else > + node_addr = si->cache_buf + OFFSET(kmem_cache_per_node) + > + (SIZE(kmem_cache_per_node_ptrs) * node) + > + OFFSET(kmem_cache_per_node_node); I suggest making the old approach the default (else) branch and the new approach the if (condition) branch: if (VALID_MEMBER(kmem_cache_per_node) && VALID_MEMBER(kmem_cache_per_node_node)) { node_addr = si->cache_buf + OFFSET(kmem_cache_per_node) + (SIZE(kmem_cache_per_node_ptrs) * node) + OFFSET(kmem_cache_per_node_node); } else { node_addr = si->cache_buf + OFFSET(kmem_cache_node) + (sizeof(void *) * node); } Since we have used the old branch for a longer time, I'd prefer anything that doesn't match the new condition to fall into the old one. Thanks, Tao Liu

> + return ULONG(node_addr); > +} > + > /* > * Emulate the total count calculation done by the > * slab_objects() sysfs function in slub.c. > @@ -19537,9 +19564,7 @@ get_kmem_cache_slub_data(long cmd, struct meminfo *si) > for (n = 0; n < vt->numnodes; n++) { > if (vt->flags & CONFIG_NUMA) { > nt = &vt->node_table[n]; > - node_ptr = ULONG(si->cache_buf + > - OFFSET(kmem_cache_node) + > - (sizeof(void *) * nt->node_id)); > + node_ptr = get_kmem_cache_node_ptr(si, nt->node_id); > } else > node_ptr = si->cache + > OFFSET(kmem_cache_local_node); > @@ -19709,9 +19734,7 @@ do_kmem_cache_slub(struct meminfo *si) > for (n = 0; n < vt->numnodes; n++) { > if (vt->flags & CONFIG_NUMA) { > nt = &vt->node_table[n]; > - node_ptr = ULONG(si->cache_buf + > - OFFSET(kmem_cache_node) + > - (sizeof(void *)* nt->node_id)); > + node_ptr = get_kmem_cache_node_ptr(si, nt->node_id); > } else > node_ptr = si->cache + > OFFSET(kmem_cache_local_node); > @@ -20515,9 +20538,7 @@ slab_to_kmem_cache_node(struct meminfo *si, ulong slab_page) > > if (vt->flags & CONFIG_NUMA) { > node = page_to_nid(slab_page); > - node_ptr = ULONG(si->cache_buf + > - OFFSET(kmem_cache_node) + > - (sizeof(void *)*node)); > + node_ptr = get_kmem_cache_node_ptr(si, node); > } else > node_ptr = si->cache + OFFSET(kmem_cache_local_node); > > diff --git a/symbols.c b/symbols.c > index a7ccdb1..652fce4 100644 > --- a/symbols.c > +++ b/symbols.c > @@ -10922,6 +10922,10 @@ dump_offset_table(char *spec, ulong makestruct) > OFFSET(kmem_cache_red_left_pad)); > fprintf(fp, " kmem_cache_node: %ld\n", > OFFSET(kmem_cache_node)); > + fprintf(fp, " kmem_cache_per_node: %ld\n", > + OFFSET(kmem_cache_per_node)); > + fprintf(fp, " kmem_cache_per_node_node: %ld\n", > + OFFSET(kmem_cache_per_node_node)); > fprintf(fp, " kmem_cache_cpu_slab: %ld\n", > OFFSET(kmem_cache_cpu_slab)); > fprintf(fp, " kmem_cache_cpu_partial: %ld\n", > @@ -12042,6 +12046,8 @@ dump_offset_table(char *spec, ulong makestruct) > SIZE(kmem_bufctl_t)); > fprintf(fp, " kmem_cache: %ld\n", SIZE(kmem_cache)); > fprintf(fp, " kmem_cache_node: %ld\n", SIZE(kmem_cache_node)); > + fprintf(fp, " kmem_cache_per_node_ptrs: %ld\n", > + SIZE(kmem_cache_per_node_ptrs)); > fprintf(fp, " kmem_cache_cpu: %ld\n", SIZE(kmem_cache_cpu)); > > fprintf(fp, " swap_info_struct: %ld\n", > -- > 2.52.0 > -- > Crash-utility mailing list -- devel(a)lists.crash-utility.osci.io > To unsubscribe send an email to devel-leave(a)lists.crash-utility.osci.io > https://urldefense.com/v3/__https://$*7Bdomain_name*7D/admin/lists/ devel.lists.crash-utility.osci.io/__;JSU!!ACWV5N9M2RV99hQ! O1Hf-3Yy5Z2kcbB75VvSaoFma69uN3QLn5J1UKeIbTvRAvowZJrHLu3BkU7jc4hhXGWmI3MhLcfPyzDp8kQ$ <https://urldefense.com/v3/__https://$*7Bdomain_name*7D/admin/lists/devel.... > Contribution Guidelines: https://urldefense.com/v3/__https://github.com/crash-utility/crash/ wiki__;!!ACWV5N9M2RV99hQ! O1Hf-3Yy5Z2kcbB75VvSaoFma69uN3QLn5J1UKeIbTvRAvowZJrHLu3BkU7jc4hhXGWmI3MhLcfPiU2f23U$ <https://urldefense.com/v3/__https://github.com/crash-utility/crash/wiki__... >