Re: [Intel-wired-lan] [PATCH] ixgbe: Use kmap_local_page in ixgbe_check_lbtest_frame()

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 9/22/2022 1:58 PM, Alexander Duyck wrote:
On Thu, Sep 22, 2022 at 1:07 PM Anirudh Venkataramanan
<anirudh.venkataramanan@xxxxxxxxx> wrote:


Following Fabio's patches, I made similar changes for e1000/e1000e and
submitted them to IWL [1].

Yesterday, Ira Weiny pointed me to some feedback from Dave Hansen on the
use of page_address() [2]. My understanding of this feedback is that
it's safer to use kmap_local_page() instead of page_address(), because
you don't always know how the underlying page was allocated.

This approach (of using kmap_local_page() instead of page_address())
makes sense to me. Any reason not to go this way?

[1]

https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20220919180949.388785-1-anirudh.venkataramanan@xxxxxxxxx/

https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20220919180949.388785-2-anirudh.venkataramanan@xxxxxxxxx/

[2]
https://lore.kernel.org/lkml/5d667258-b58b-3d28-3609-e7914c99b31b@xxxxxxxxx/

Ani

For the two patches you referenced the driver is the one allocating
the pages. So in such a case the page_address should be acceptable.
Specifically we are falling into alloc_page(GFP_ATOMIC) which should
fall into the first case that Dave Hansen called out.

Right. However, I did run into a case in the chelsio inline crypto driver where it seems like the pages are allocated outside the driver. In such cases, kmap_local_page() would be the right approach, as the driver can't make assumptions on how the page was allocated.

... and this makes me wonder why not just use kmap_local_page() even in cases where the page allocation was done in the driver. IMO, this is simpler because

a) you don't have to care how a page was allocated. kmap_local_page() will create a temporary mapping if required, if not it just becomes a wrapper to page_address().

b) should a future patch change the allocation to be from highmem, you don't have to change a bunch of page_address() calls to be kmap_local_page().

Is using page_address() directly beneficial in some way?

Ani




[Index of Archives]     [Linux Samsung SoC]     [Linux Rockchip SoC]     [Linux Actions SoC]     [Linux for Synopsys ARC Processors]     [Linux NFS]     [Linux NILFS]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]


  Powered by Linux