On 04.10.21 15:45, Matthew Wilcox (Oracle) wrote:
Make struct slab independent of struct page. It still uses the
underlying memory in struct page for storing slab-specific data,
but slab and slub can now be weaned off using struct page directly.
Some of the wrapper functions (slab_address() and slab_order())
still need to cast to struct page, but this is a significant
disentanglement.
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
include/linux/mm_types.h | 56 +++++++++++++++++++++++++++++
include/linux/page-flags.h | 29 +++++++++++++++
mm/slab.h | 73 ++++++++++++++++++++++++++++++++++++++
mm/slub.c | 8 ++---
4 files changed, 162 insertions(+), 4 deletions(-)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 7f8ee09c711f..c2ea71aba84e 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -239,6 +239,62 @@ struct page {
#endif
} _struct_page_alignment;
+/* Reuses the bits in struct page */
+struct slab {
+ unsigned long flags;
+ union {
+ struct list_head slab_list;
+ struct { /* Partial pages */
+ struct slab *next;
+#ifdef CONFIG_64BIT
+ int slabs; /* Nr of slabs left */
+ int pobjects; /* Approximate count */
+#else
+ short int slabs;
+ short int pobjects;
+#endif
+ };
+ struct rcu_head rcu_head;
+ };
+ struct kmem_cache *slab_cache; /* not slob */
+ /* Double-word boundary */
+ void *freelist; /* first free object */
+ union {
+ void *s_mem; /* slab: first object */
+ unsigned long counters; /* SLUB */
+ struct { /* SLUB */
+ unsigned inuse:16;
+ unsigned objects:15;
+ unsigned frozen:1;
+ };
+ };
+
+ union {
+ unsigned int active; /* SLAB */
+ int units; /* SLOB */
+ };
+ atomic_t _refcount;
+#ifdef CONFIG_MEMCG
+ unsigned long memcg_data;
+#endif
+};
My 2 cents just from reading the first 3 mails:
I'm not particularly happy about the "/* Reuses the bits in struct page
*/" part of thingy here, essentially really having to pay attention what
whenever we change something in "struct page" to not mess up all the
other special types we have. And I wasn't particularly happy scanning
patch #1 and #2 for the same reason. Can't we avoid that?
What I can see is that we want (and must right now for generic
infrastructure) keep some members of the the struct page" (e.g., flags,
_refcount) at the very same place, because generic infrastructure relies
on them.
Maybe that has already been discussed somewhere deep down in folio mail
threads, but I would have expected that we keep struct-page generic
inside struct-page and only have inside "struct slab" what's special for
"struct slab".
I would have thought that we want something like this (but absolutely
not this):
struct page_header {
unsigned long flags;
}
struct page_footer {
atomic_t _refcount;
#ifdef CONFIG_MEMCG
unsigned long memcg_data;
#endif
}
struct page {
struct page_header header;
uint8_t reserved[$DO_THE_MATH]
struct page_footer footer;
};
struct slab {
...
};
struct slab_page {
struct page_header header;
struct slab;
struct page_footer footer;
};
Instead of providing helpers for struct slab_page, simply cast to struct
page and replace the structs in struct slab_page by simple placeholders
with the same size.
That would to me look like a nice cleanup itself, ignoring all the other
parallel discussions that are going on. But I imagine the problem is
more involved, and a simple header/footer might not be sufficient.
--
Thanks,
David / dhildenb
