Messages in this thread | | | Date | Thu, 22 Sep 2022 15:38:02 -0700 | Subject | Re: [Intel-wired-lan] [PATCH] ixgbe: Use kmap_local_page in ixgbe_check_lbtest_frame() | From | Anirudh Venkataramanan <> |
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On 9/22/2022 1:58 PM, Alexander Duyck wrote: > On Thu, Sep 22, 2022 at 1:07 PM Anirudh Venkataramanan > <anirudh.venkataramanan@intel.com> 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@intel.com/ >> >> https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20220919180949.388785-2-anirudh.venkataramanan@intel.com/ >> >> [2] >> https://lore.kernel.org/lkml/5d667258-b58b-3d28-3609-e7914c99b31b@intel.com/ >> >> 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
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