From: Seth Jennings <sjenning@linux.vnet.ibm.com>
To: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>,
Nitin Gupta <ngupta@vflare.org>,
Dan Magenheimer <dan.magenheimer@oracle.com>,
Brian King <brking@linux.vnet.ibm.com>,
Konrad Wilk <konrad.wilk@oracle.com>,
linux-mm@kvack.org, devel@driverdev.osuosl.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/5] staging: zsmalloc: zsmalloc memory allocation library
Date: Mon, 06 Feb 2012 11:26:25 -0600 [thread overview]
Message-ID: <4F300D41.5050105@linux.vnet.ibm.com> (raw)
In-Reply-To: <4F21A5AF.6010605@linux.vnet.ibm.com>
On 01/26/2012 01:12 PM, Dave Hansen wrote:
> On 01/09/2012 02:51 PM, Seth Jennings wrote:
>> + area = &get_cpu_var(zs_map_area);
>> + if (off + class->size <= PAGE_SIZE) {
>> + /* this object is contained entirely within a page */
>> + area->vm_addr = kmap_atomic(page);
>> + } else {
>> + /* this object spans two pages */
>> + struct page *nextp;
>> +
>> + nextp = get_next_page(page);
>> + BUG_ON(!nextp);
>> +
>> +
>> + set_pte(area->vm_ptes[0], mk_pte(page, PAGE_KERNEL));
>> + set_pte(area->vm_ptes[1], mk_pte(nextp, PAGE_KERNEL));
>> +
>> + /* We pre-allocated VM area so mapping can never fail */
>> + area->vm_addr = area->vm->addr;
>> + }
>
> This bit appears to be trying to make kmap_atomic() variant that can map
> two pages in to contigious virtual addresses. Instead of open-coding it
> in a non-portable way like this, should we just make a new kmap_atomic()
> variant that does this?
>
> From the way it's implemented, I _think_ you're guaranteed to get two
> contiguous addresses if you do two adjacent kmap_atomics() on the same CPU:
>
> void *kmap_atomic_prot(struct page *page, pgprot_t prot)
> {
> ...
> type = kmap_atomic_idx_push();
> idx = type + KM_TYPE_NR*smp_processor_id();
> vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
>
> I think if you do a get_cpu()/put_cpu() or just a preempt_disable()
> across the operations you'll be guaranteed to get two contiguous addresses.
I'm not quite following here. kmap_atomic() only does this for highmem pages.
For normal pages (all pages for 64-bit), it doesn't do any mapping at all. It
just returns the virtual address of the page since it is in the kernel's address
space.
For this design, the pages _must_ be mapped, even if the pages are directly
reachable in the address space, because they must be virtually contiguous.
--
Seth
next prev parent reply other threads:[~2012-02-06 17:27 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-09 22:51 [PATCH 0/5] staging: zsmalloc: memory allocator for compressed pages Seth Jennings
2012-01-09 22:51 ` [PATCH 1/5] staging: zsmalloc: zsmalloc memory allocation library Seth Jennings
2012-01-20 22:12 ` Andrew Morton
2012-01-23 14:36 ` Seth Jennings
2012-01-23 18:57 ` Nitin Gupta
2012-01-23 19:40 ` Andrew Morton
2012-01-26 19:12 ` Dave Hansen
2012-02-06 17:26 ` Seth Jennings [this message]
2012-02-08 16:39 ` Dave Hansen
2012-02-08 17:15 ` Dan Magenheimer
2012-02-08 17:21 ` Dave Hansen
2012-02-08 17:53 ` Nitin Gupta
2012-02-08 18:28 ` Dave Hansen
2012-02-08 20:57 ` Nitin Gupta
2012-02-08 21:39 ` Dan Magenheimer
2012-02-08 23:07 ` Dave Hansen
2012-01-09 22:51 ` [PATCH 2/5] staging: add zsmalloc to Kconfig/Makefile Seth Jennings
2012-01-09 22:51 ` [PATCH 3/5] staging: zcache: replace xvmalloc with zsmalloc Seth Jennings
2012-02-09 1:13 ` Greg KH
2012-02-09 14:36 ` Seth Jennings
2012-02-09 14:55 ` Seth Jennings
2012-02-09 18:13 ` Greg KH
2012-02-09 18:28 ` Seth Jennings
2012-01-09 22:51 ` [PATCH 4/5] staging: zram: " Seth Jennings
2012-01-09 22:52 ` [PATCH 5/5] staging: zram: remove xvmalloc Seth Jennings
2012-01-09 23:09 ` [PATCH 0/5] staging: zsmalloc: memory allocator for compressed pages Greg KH
2012-01-09 23:26 ` Seth Jennings
2012-01-20 22:03 ` Andrew Morton
2012-01-23 14:27 ` Seth Jennings
[not found] <<1326149520-31720-1-git-send-email-sjenning@linux.vnet.ibm.com>
[not found] ` <<1326149520-31720-2-git-send-email-sjenning@linux.vnet.ibm.com>
2012-01-11 17:19 ` [PATCH 1/5] staging: zsmalloc: zsmalloc memory allocation library Dan Magenheimer
2012-01-11 17:45 ` Seth Jennings
2012-01-11 21:44 ` Dan Magenheimer
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:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4F300D41.5050105@linux.vnet.ibm.com \
--to=sjenning@linux.vnet.ibm.com \
--cc=brking@linux.vnet.ibm.com \
--cc=dan.magenheimer@oracle.com \
--cc=dave@linux.vnet.ibm.com \
--cc=devel@driverdev.osuosl.org \
--cc=gregkh@suse.de \
--cc=konrad.wilk@oracle.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=ngupta@vflare.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* 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).