On 18.10.24 12:46, Matthew Wilcox wrote:
On Tue, Oct 08, 2024 at 04:16:39PM +0200, David Hildenbrand wrote:
4. Make sure that we're good with memcg_data. I think we are (it's only
used in folios and slabs today, I _think_), but it'll be good to be
sure. Someone who understands memcg better than I do can probably find
some stuff to clean up.
Last time I looked at this (1month ago), I had the same impression.
I took a shot at this. The problem is mm/page_alloc.c:
__alloc_pages_noprof:
if (memcg_kmem_online() && (gfp & __GFP_ACCOUNT) && page &&
unlikely(__memcg_kmem_charge_page(page, gfp, order) != 0)) {
__free_pages(page, order);
page = NULL;
}
Right, I recall that we are only touching the first page. IIRC, it's not
necessarily a compound page.
I think someone (maybe Yosry?) tried to explain this problem to me at
LSFMM, but I didn't understand.
Most of the places that use GFP_KERNEL_ACCOUNT are either page tables
or kmalloc/kvmalloc. But I think we're going to need a new memdesc
type for accounted memory.
struct accounted_mem {
unsigned long flags;
struct obj_cgroup *objcg;
};
(we'll be able to drop MEMCG_DATA_* once we have the memdesc type, but
we need to keep it until we're there).
So I guess that's my next step -- adding:
struct accounted_mem {
unsigned long flags;
unsigned long padding[5];
unsigned int padding2[2];
unsigned long objcg;
};
and the various assertions that objcg & flags occupy the same bytes in
accounted_mem as they do in page, until we separate them entirely.
But how to do that without a compound page?
--
Cheers,
David / dhildenb
