Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Mon, 8 Jun 2020 14:25:03 +0200 | Subject | Re: [PATCH] dma-pool: Fix too large DMA pools on medium systems |
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Hi Robin,
On Mon, Jun 8, 2020 at 2:04 PM Robin Murphy <robin.murphy@arm.com> wrote: > On 2020-06-08 09:52, Geert Uytterhoeven wrote: > > On systems with at least 32 MiB, but less than 32 GiB of RAM, the DMA > > memory pools are much larger than intended (e.g. 2 MiB instead of 128 > > KiB on a 256 MiB system). > > > > Fix this by correcting the calculation of the number of GiBs of RAM in > > the system. > > > > Fixes: 1d659236fb43c4d2 ("dma-pool: scale the default DMA coherent pool size with memory capacity") > > Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> > --- a/kernel/dma/pool.c > > +++ b/kernel/dma/pool.c > > @@ -175,8 +175,8 @@ static int __init dma_atomic_pool_init(void) > > * sizes to 128KB per 1GB of memory, min 128KB, max MAX_ORDER-1. > > */ > > if (!atomic_pool_size) { > > - atomic_pool_size = max(totalram_pages() >> PAGE_SHIFT, 1UL) * > > - SZ_128K; > > + unsigned long gigs = totalram_pages() >> (30 - PAGE_SHIFT); > > + atomic_pool_size = max(gigs, 1UL) * SZ_128K; > > atomic_pool_size = min_t(size_t, atomic_pool_size, > > 1 << (PAGE_SHIFT + MAX_ORDER-1)); > > } > > Nit: although this probably is right, it seems even less readable than
">> (x - PAGE_SHIFT)" is a commonly used construct in the kernel.
> the broken version (where at least some at-a-glance 'dimensional > analysis' flags up "(number of pages) >> PAGE_SHIFT" as rather > suspicious). How about a something a little more self-explanatory, e.g.: > > unsigned long pages = totalram_pages() * SZ_128K / SZ_1GB;
That multiplication will overflow on 32-bit systems (perhaps even on large 64-bit systems; any 47-bit addressing?).
unsigned long pages = totalram_pages() / (SZ_1GB / SZ_128K);
> atomic_pool_size = min(pages, MAX_ORDER_NR_PAGES) << PAGE_SHIFT; > atomic_pool_size = max_t(size_t, atomic_pool_size, SZ_128K);
I agree this part is an improvement.
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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