archive mirror
 help / color / mirror / Atom feed
From: Vlastimil Babka <>
To: Ioana Ciornei <>, Kevin Hao <>
Cc: "David S . Miller" <>,
	Jakub Kicinski <>,
	Andrew Morton <>,
	"" <>,
	"" <>,
	Eric Dumazet <>
Subject: Re: [PATCH net-next v2 1/4] mm: page_frag: Introduce page_frag_alloc_align()
Date: Tue, 2 Feb 2021 12:48:28 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20210202113618.s4tz2q7ysbnecgsl@skbuf>

On 2/2/21 12:36 PM, Ioana Ciornei wrote:
> On Sun, Jan 31, 2021 at 03:44:23PM +0800, Kevin Hao wrote:
>> In the current implementation of page_frag_alloc(), it doesn't have
>> any align guarantee for the returned buffer address. But for some
>> hardwares they do require the DMA buffer to be aligned correctly,
>> so we would have to use some workarounds like below if the buffers
>> allocated by the page_frag_alloc() are used by these hardwares for
>> DMA.
>>     buf = page_frag_alloc(really_needed_size + align);
>>     buf = PTR_ALIGN(buf, align);
>> These codes seems ugly and would waste a lot of memories if the buffers
>> are used in a network driver for the TX/RX.
> Isn't the memory wasted even with this change?

Yes, but less of it. Not always full amount of align, but up to it. Perhaps even

> I am not familiar with the frag allocator so I might be missing
> something, but from what I understood each page_frag_cache keeps only
> the offset inside the current page being allocated, offset which you
> ALIGN_DOWN() to match the alignment requirement. I don't see how that
> memory between the non-aligned and aligned offset is going to be used
> again before the entire page is freed.

True, thath's how page_frag is designed. The align amounts would be most likely
too small to be usable anyway.

  reply	other threads:[~2021-02-02 11:48 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-31  7:44 [PATCH net-next v2 0/4] net: Avoid the memory waste in some Ethernet drivers Kevin Hao
2021-01-31  7:44 ` [PATCH net-next v2 1/4] mm: page_frag: Introduce page_frag_alloc_align() Kevin Hao
2021-02-02 11:36   ` Ioana Ciornei
2021-02-02 11:48     ` Vlastimil Babka [this message]
2021-02-02 12:31       ` Ioana Ciornei
2021-02-02 16:19   ` Alexander Duyck
2021-02-04  6:40     ` Kevin Hao

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).