linux-kernel - Re: [PATCH] dma-debug: increase HASH

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Date:   Thu, 30 Jan 2020 17:27:40 +0100
From:   Christoph Hellwig <hch@....de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Eric Dumazet <edumazet@...gle.com>, Christoph Hellwig <hch@....de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH] dma-debug: increase HASH_SIZE

On Tue, Dec 10, 2019 at 03:55:08PM +0100, Geert Uytterhoeven wrote:
> On Wed, Oct 30, 2019 at 8:13 PM Eric Dumazet <edumazet@...gle.com> wrote:
> > With modern NIC, it is not unusual having about ~256,000 active dma
> > mappings. Hash size of 1024 buckets is too small.
> >
> > Forcing full cache line per bucket does not seem useful,
> > especially now that we have a contention on free_entries_lock
> > for allocations and freeing of entries. Better using space
> > to fit more buckets.
> >
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Cc: Christoph Hellwig <hch@....de>
> > Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> > ---
> >  kernel/dma/debug.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
> > index 4ad74f5987ea9e95f9bb5e2d1592254e367d24fb..35e2a853bff9c482d789ab331d79aaee07753a97 100644
> > --- a/kernel/dma/debug.c
> > +++ b/kernel/dma/debug.c
> > @@ -27,7 +27,7 @@
> >
> >  #include <asm/sections.h>
> >
> > -#define HASH_SIZE       1024ULL
> > +#define HASH_SIZE       16384ULL
> >  #define HASH_FN_SHIFT   13
> >  #define HASH_FN_MASK    (HASH_SIZE - 1)
> >
> > @@ -87,7 +87,7 @@ typedef bool (*match_fn)(struct dma_debug_entry *, struct dma_debug_entry *);
> >  struct hash_bucket {
> >         struct list_head list;
> >         spinlock_t lock;
> > -} ____cacheline_aligned_in_smp;
> > +};
> >
> >  /* Hash list to save the allocated dma addresses */
> >  static struct hash_bucket dma_entry_hash[HASH_SIZE];
> 
> JFTR, this increases dma_entry_hash size by 327680 bytes, and pushes
> a few more boards beyond their bootloader-imposed kernel size limits.
> 
> Disabling CONFIG_DMA_API_DEBUG fixes that.
> Of course the real fix is to fix the bootloaders...

Can someone just send a patch to switch this to a dynamic allocation?