Re: [PATCH] io_uring/rsrc: remove registered buffer 1GB limit

[Jens Axboe <axboe@kernel.dk>]

On 5/5/26 7:23 AM, Cl?ment L?ger wrote:
> On 5/5/26 12:09, Jens Axboe wrote:
>> > On 5/5/26 1:39 AM, Jens Axboe wrote:
>>> There's no real reason to have a limit, as the memory is accounted by
>>> the lockmem limits anyway, if any exist. io_pin_pages() will still
>>> restrict the maximum allowed limit per buffer, which is INT_MAX
>>> number of pages. For a 4kb page size system, the limit is 8TB.
>>>
>>> Reported-by: Andres Freund <andres@anarazel.de>
>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>
>> Forgot that I had a prep patch for this one... The branch is here:
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux.git/log/?h=io_uring-reg-buffers
>>
>> and notably the patch before this one is below, which bumps the ->len
>> size of the io_mapped_ubuf. I'll send this out as a proper series later
>> this week, this is 7.2 material obviously.
>>
>> commit 381e736515173a1fb78d2a86983d3ebfcf263597
>> Author: Jens Axboe <axboe@kernel.dk>
>> Date:   Mon May 4 05:40:16 2026 -0600
>>
>>      io_uring/rsrc: bump struct io_mapped_ubuf length field to size_t
>>           In preparation for supporting bigger individual buffers, bump the length
>>      field to a full 8-bytes with size_t rather than an unsigned int.
>>           Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>
>> diff --git a/io_uring/fdinfo.c b/io_uring/fdinfo.c
>> index c2d3e45544bb..f0ff4bd01b6d 100644
>> --- a/io_uring/fdinfo.c
>> +++ b/io_uring/fdinfo.c
>> @@ -223,7 +223,7 @@ static void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, struct seq_file *m)
>>           if (ctx->buf_table.nodes[i])
>>               buf = ctx->buf_table.nodes[i]->buf;
>>           if (buf)
>> -            seq_printf(m, "%5u: 0x%llx/%u\n", i, buf->ubuf, buf->len);
>> +            seq_printf(m, "%5u: 0x%llx/%zu\n", i, buf->ubuf, buf->len);
>>           else
>>               seq_printf(m, "%5u: <none>\n", i);
>>       }
>> diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
>> index 44e3386f7c1c..03521b50926c 100644
>> --- a/io_uring/rsrc.h
>> +++ b/io_uring/rsrc.h
>> @@ -34,15 +34,15 @@ enum {
>>     struct io_mapped_ubuf {
>>       u64        ubuf;
>> -    unsigned int    len;
>> +    size_t        len;
>>       unsigned int    nr_bvecs;
>>       unsigned int    folio_shift;
>>       refcount_t    refs;
>> +    u8        flags;
>> +    u8        dir;
>>       unsigned long    acct_pages;
>>       void        (*release)(void *);
>>       void        *priv;
>> -    u8        flags;
>> -    u8        dir;
> 
> Hi Jens,
> 
> This seems like an unrelated change.

Hmm, how so? It's required for removing the 1GB restriction, as it bumps
buf->len from a 32-bit unsigned to a 64-bit size_t.

Oh you mean moving flags and dir? That's just so it packs better,
changing int would leave a 4-byte gap. Might as well move flags and dir
near the 4b refcount_t to avoid bloating the struct.

-- 
Jens Axboe