On Mon, Jan 25, 2021 at 05:54:51PM +0100, Michal Hocko wrote:

On Thu 21-01-21 14:27:20, Mike Rapoport wrote:

quoted

From: Mike Rapoport <redacted>

Account memory consumed by secretmem to memcg. The accounting is updated
when the memory is actually allocated and freed.

What does this mean?

That means that the accounting is updated when secretmem does cma_alloc()
and cma_relase().

What are the lifetime rules?

Hmm, what do you mean by lifetime rules?

[...]

quoted

+static int secretmem_account_pages(struct page *page, gfp_t gfp, int order)
+{
+	int err;
+
+	err = memcg_kmem_charge_page(page, gfp, order);
+	if (err)
+		return err;
+
+	/*
+	 * seceremem caches are unreclaimable kernel allocations, so treat
+	 * them as unreclaimable slab memory for VM statistics purposes
+	 */
+	mod_lruvec_page_state(page, NR_SLAB_UNRECLAIMABLE_B,
+			      PAGE_SIZE << order);

A lot of memcg accounted memory is not reclaimable. Why do you abuse
SLAB counter when this is not a slab owned memory? Why do you use the
kmem accounting API when __GFP_ACCOUNT should give you the same without
this details?

I cannot use __GFP_ACCOUNT because cma_alloc() does not use gfp.
Besides, kmem accounting with __GFP_ACCOUNT does not seem
to update stats and there was an explicit request for statistics:
 
https://lore.kernel.org/lkml/CALo0P13aq3GsONnZrksZNU9RtfhMsZXGWhK1n=xYJWQizCd4Zw@mail.gmail.com/ (local)

As for (ab)using NR_SLAB_UNRECLAIMABLE_B, as it was already discussed here:

https://lore.kernel.org/lkml/20201129172625.GD557259@kernel.org/ (local)

I think that a dedicated stats counter would be too much at the moment and
NR_SLAB_UNRECLAIMABLE_B is the only explicit stat for unreclaimable memory.

-- 
Sincerely yours,
Mike.

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