Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN

On Wed, Apr 20, 2022 at 12:08 PM Catalin Marinas
[off-list ref] wrote:

With kstrdup() modified to pass __GFP_PACKED (as per the last hunk in
the diff below), I get just after boot:

kmalloc-128         8966   9056    128   32
kmalloc-96             0      0     96   42
kmalloc-64           192    192     64   64
kmalloc-32           768    768     32  128
kmalloc-16          2048   2048     16  256
kmalloc-8           2560   2560      8  512

So that's probably the simplest approach and using the ftrace histogram
we can add the flag to more places.

I agree that this seems to be the safest thing to do, and maybe
__GFP_PACKED is a better flag name than __GFP_NODMA.

That said, It worries me a bit in that to me "PACKED" implies "no
alignment at all". And I could _easily_ see people still wanting to do
8-byte allocations that have 8-byte alignment because it's some kind
of private pointer thing or whatever.

For "kstrdup()", a flag like __GFP_PACKED makes 100% sense, since it
literally wants byte alignment.

But what about those "random small structures" cases?

Anyway, I'm perfectly happy calling it __GFP_PACKED, but at a minimum
document that "packed" in this case still means "__alignof__(unsigned
long long)" or something like that?

                      Linus

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