Messages in this thread | | | Date | Fri, 21 Aug 2020 14:14:00 -0700 (PDT) | Subject | Re: [PATCH] net: bypass ->sendpage for slab pages | From | David Miller <> |
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From: Christoph Hellwig <hch@lst.de> Date: Thu, 20 Aug 2020 06:37:44 +0200
> If you look at who uses sendpage outside the networking layer itself > you see that it is basically block driver and file systems. These > have no way to control what memory they get passed and have to deal > with everything someone throws at them.
I see nvme doing virt_to_page() on several things when it calls into kernel_sendpage().
This is the kind of stuff I want cleaned up, and which your patch will not trap nor address.
In nvme it sometimes seems to check for sendpage validity:
/* can't zcopy slab pages */ if (unlikely(PageSlab(page))) { ret = sock_no_sendpage(queue->sock, page, offset, len, flags); } else { ret = kernel_sendpage(queue->sock, page, offset, len, flags); }
Yet elsewhere does not and just blindly calls:
ret = kernel_sendpage(queue->sock, virt_to_page(pdu), offset_in_page(pdu) + req->offset, len, flags);
This pdu seems to come from a page frag allocation.
That's the target side. On the host side:
ret = kernel_sendpage(cmd->queue->sock, page, cmd->offset, left, flags);
No page slab check or anything like that.
I'm hesitent to put in the kernel_sendpage() patch, becuase it provides a disincentive to fix up code like this.
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