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Date: Wed, 10 Aug 2011 09:44:21 -0500
From: Seth Jennings <sjenning@...ux.vnet.ibm.com>
To: Dan Magenheimer <dan.magenheimer@...cle.com>
CC: Greg Kroah-Hartman <gregkh@...e.de>,
Marcus Klemm <marcus.klemm@...glemail.com>,
Konrad Wilk <konrad.wilk@...cle.com>,
linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
kvm@...r.kernel.org, linux-mm <linux-mm@...ck.org>,
Brian King <brking@...ux.vnet.ibm.com>,
Robert Jennings <rcj@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2] staging: zcache: support multiple clients, prep for
KVM and RAMster
On 08/10/2011 09:21 AM, Seth Jennings wrote:
> On 06/30/2011 02:01 PM, Dan Magenheimer wrote:
>> Hi Greg --
>>
>> I think this patch is now ready for staging-next and for merging when
>> the 3.1 window opens. Please let me know if you need any logistics
>> done differently.
>>
>> Thanks,
>> Dan
>>
>> ===
>>
>>> From: Dan Magenheimer <dan.magenheimer@...cle.com>
>> Subject: staging: zcache: support multiple clients, prep for KVM and RAMster
>>
>> This is version 2 of an update to zcache, incorporating feedback from the list.
>> This patch adds support to the in-kernel transcendent memory ("tmem") code
>> and the zcache driver for multiple clients, which will be needed for both
>> RAMster and KVM support. It also adds additional tmem callbacks to support
>> RAMster and corresponding no-op stubs in the zcache driver. In v2, I've
>> also taken the liberty of adding some additional sysfs variables to
>> both surface information and allow policy control. Those experimenting
>> with zcache should find them useful.
>>
>> Signed-off-by: Dan Magenheimer <dan.magenheimer@...cle.com>
>>
>> [v2: konrad.wilk@...cle.com: fix bools, add check for NULL, fix a comment]
>> [v2: sjenning@...ux.vnet.ibm.com: add info/tunables for poor compression]
>> [v2: marcusklemm@...glemail.com: add tunable for max persistent pages]
>> Cc: Nitin Gupta <ngupta@...are.org>
>> Cc: linux-mm@...ck.org
>> Cc: kvm@...r.kernel.org
>>
>> ===
>>
>> Diffstat:
>> drivers/staging/zcache/tmem.c | 100 +++-
>> drivers/staging/zcache/tmem.h | 23
>> drivers/staging/zcache/zcache.c | 512 +++++++++++++++++----
>> 3 files changed, 520 insertions(+), 115 deletions(-)
>>
>>
> <cut>
>> @@ -901,48 +1144,59 @@ static unsigned long zcache_curr_pers_pa
>> /* forward reference */
>> static int zcache_compress(struct page *from, void **out_va, size_t *out_len);
>>
>> -static void *zcache_pampd_create(struct tmem_pool *pool, struct tmem_oid *oid,
>> - uint32_t index, struct page *page)
>> +static void *zcache_pampd_create(char *data, size_t size, bool raw, int eph,
>> + struct tmem_pool *pool, struct tmem_oid *oid,
>> + uint32_t index)
>> {
>> void *pampd = NULL, *cdata;
>> size_t clen;
>> int ret;
>> - bool ephemeral = is_ephemeral(pool);
>> unsigned long count;
>> + struct page *page = virt_to_page(data);
>
> With zcache_put_page() modified to pass page_address(page) instead of the
> actual page structure, in combination with the function signature changes
> to tmem_put() and zcache_pampd_create(), zcache_pampd_create() tries to
> (re)derive the page structure from the virtual address. However, if the
> original page is a high memory page (or any unmapped page), this
> virt_to_page() fails because the page_address() in zcache_put_page()
> returned NULL.
>
> With CONFIG_DEBUG_VIRTUAL set, the BUG message is this:
> ==========
> [ 101.347711] ------------[ cut here ]------------
> [ 101.348030] kernel BUG at arch/x86/mm/physaddr.c:51!
> [ 101.348030] invalid opcode: 0000 [#1] DEBUG_PAGEALLOC
> [ 101.348030] Modules linked in:
> [ 101.348030]
> [ 101.348030] Pid: 20, comm: kswapd0 Not tainted 3.1.0-rc1+ #229 Bochs Bochs
> [ 101.348030] EIP: 0060:[<c1058c9a>] EFLAGS: 00010013 CPU: 0
> [ 101.348030] EIP is at __phys_addr+0x1a/0x50
> [ 101.348030] EAX: 00000000 EBX: f5e64000 ECX: 00000000 EDX: 00001000
> [ 101.348030] ESI: f6ffd000 EDI: 00000000 EBP: f6353c10 ESP: f6353c10
> [ 101.348030] DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068
> [ 101.348030] Process kswapd0 (pid: 20, ti=f6352000 task=f69b9c20 task.ti=f6352000)
> [ 101.348030] Stack:
> [ 101.348030] f6353c60 c12e4114 00000000 00000001 00000000 c12e5682 00000000 00000046
> [ 101.348030] 00000000 f5e65668 f5e65658 f5e65654 f580f000 f6353c60 c13904f5 00000000
> [ 101.348030] f5e65654 f5e64000 f5eab000 00000000 f6353cb0 c12e5713 00000000 f5e64000
> [ 101.348030] Call Trace:
> [ 101.348030] [<c12e4114>] zcache_pampd_create+0x14/0x6a0
> [ 101.348030] [<c12e5682>] ? tmem_put+0x52/0x3f0
> [ 101.348030] [<c13904f5>] ? _raw_spin_lock+0x45/0x50
> [ 101.348030] [<c12e5713>] tmem_put+0xe3/0x3f0
> [ 101.348030] [<c10f5358>] ? page_address+0xb8/0xe0
> [ 101.348030] [<c12e498b>] zcache_frontswap_put_page+0x1eb/0x2e0
> [ 101.348030] [<c110798b>] __frontswap_put_page+0x6b/0x110
> [ 101.348030] [<c1103ccf>] swap_writepage+0x8f/0xf0
> [ 101.348030] [<c10ee377>] shmem_writepage+0x1a7/0x1d0
> [ 101.348030] [<c10ea907>] shrink_page_list+0x3f7/0x7c0
> [ 101.348030] [<c10eafdd>] shrink_inactive_list+0x12d/0x360
> [ 101.348030] [<c10eb5f8>] shrink_zone+0x3e8/0x530
> [ 101.348030] [<c10ebc92>] kswapd+0x552/0x940
> [ 101.348030] [<c1084460>] ? wake_up_bit+0x30/0x30
> [ 101.348030] [<c10eb740>] ? shrink_zone+0x530/0x530
> [ 101.348030] [<c10840e4>] kthread+0x74/0x80
> [ 101.348030] [<c1084070>] ? __init_kthread_worker+0x60/0x60
> [ 101.348030] [<c1397736>] kernel_thread_helper+0x6/0xd
> [ 101.348030] Code: 00 c0 ff 81 eb 00 20 00 00 39 d8 72 cd eb ae 66 90 55 3d ff ff ff bf 89 e5 76 10 80 3d 10 88 53 c1 00 75 09 05 00 00 00 40 5d c3 <0f> 0b 8b 15 b0 6a 9e c1 81 c2 00 00 80 00 39 d0 72 e7 8b 15 a8
> [ 101.348030] EIP: [<c1058c9a>] __phys_addr+0x1a/0x50 SS:ESP 0068:f6353c10
> ==========
>
> This crash is hit every time a high memory page is swapped out.
>
> I have no solution right now other that to revert this patch and
> restore the original signatures.
>
Sorry for the noise, but I noticed right after I sent this that
the tmem layer doesn't DO anything with the data parameter. So
a possible solution is to just pass the page pointer instead of
the virtual address. After all, pointers are pointers.
--- a/drivers/staging/zcache/zcache.c
+++ b/drivers/staging/zcache/zcache.c
@@ -1153,7 +1153,7 @@ static void *zcache_pampd_create(char *data, size_t size,
size_t clen;
int ret;
unsigned long count;
- struct page *page = virt_to_page(data);
+ struct page *page = (struct page *)(data);
struct zcache_client *cli = pool->client;
uint16_t client_id = get_client_id_from_client(cli);
unsigned long zv_mean_zsize;
@@ -1220,7 +1220,7 @@ static int zcache_pampd_get_data(char *data, size_t *bufsi
int ret = 0;
BUG_ON(is_ephemeral(pool));
- zv_decompress(virt_to_page(data), pampd);
+ zv_decompress((struct page *)(data), pampd);
return ret;
}
@@ -1532,7 +1532,7 @@ static int zcache_put_page(int cli_id, int pool_id, struct
goto out;
if (!zcache_freeze && zcache_do_preload(pool) == 0) {
/* preload does preempt_disable on success */
- ret = tmem_put(pool, oidp, index, page_address(page),
+ ret = tmem_put(pool, oidp, index, (char *)(page),
PAGE_SIZE, 0, is_ephemeral(pool));
if (ret < 0) {
if (is_ephemeral(pool))
@@ -1565,7 +1565,7 @@ static int zcache_get_page(int cli_id, int pool_id, struct
pool = zcache_get_pool_by_id(cli_id, pool_id);
if (likely(pool != NULL)) {
if (atomic_read(&pool->obj_count) > 0)
- ret = tmem_get(pool, oidp, index, page_address(page),
+ ret = tmem_get(pool, oidp, index, (char *)(page),
&size, 0, is_ephemeral(pool));
zcache_put_pool(pool);
}
I tested this and it works.
Dan, does this mess anything else up?
> What was the rationale for the signature changes?
>
> --
> Seth
>
> --
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