Re: [PATCH 2/2] staging/lustre: use __vmalloc_node() to avoid __GFP_FS default

[Oleg Drokin <green@linuxhacker.ru>]

On Feb 2, 2015, at 12:48 PM, David Rientjes wrote:

> On Sun, 1 Feb 2015, green@linuxhacker.ru wrote:
> 
>> From: Bruno Faccini <bruno.faccini@intel.com>
>> 
>> When possible, try to use of __vmalloc_node() instead of
>> vzalloc/vzalloc_node which allows for protection flag specification,
>> and particularly to not set __GFP_FS, which can cause some deadlock
>> situations in our code due to recursive calls.
> You're saying that all usage of OBD_ALLOC_LARGE() and 
> OBD_CPT_ALLOC_LARGE() are in contexts where we need GFP_NOFS?  It would be 

Most of them fore sure (hm, there's only one OBD_CPT_ALLOC_LARGE in the client
and I imagine it better be GFP_NOFS even though the condition for that is
very unlikely, but that's what happens when you have tens of thousands nodes
all doing the same code all the time - all sorts of unlikely things trigger a lot).

> much better to keep using vzalloc{,_node)() in contexts that permit 
> __GFP_FS for a higher likelihood of being able to allocate the memory.

While it's certainly possible to go audit all the OBD_ALLOC_LARGE and
isolate the ones where __GFP_FS is not detrimential, I just found yesterday that
vmalloc possibly does GFP_KERNEL allocations in its guts no matter what.
I saw all the rants and stuff about that too (but somewhat old).
Yet I cannot help but ask too if perhaps something could be done about it now?

> 
>> Additionally fixed a typo in the macro name: VEROBSE->VERBOSE
>> 
>> Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
>> Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
>> Reviewed-on: http://review.whamcloud.com/11190
>> Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5349
>> ---
>> drivers/staging/lustre/lustre/include/obd_support.h | 18 ++++++++++++------
>> 1 file changed, 12 insertions(+), 6 deletions(-)
>> 
>> diff --git a/drivers/staging/lustre/lustre/include/obd_support.h b/drivers/staging/lustre/lustre/include/obd_support.h
>> index 2991d2e..c90a88e 100644
>> --- a/drivers/staging/lustre/lustre/include/obd_support.h
>> +++ b/drivers/staging/lustre/lustre/include/obd_support.h
>> @@ -655,11 +655,17 @@ do {									      \
>> #define OBD_CPT_ALLOC_PTR(ptr, cptab, cpt)				      \
>> 	OBD_CPT_ALLOC(ptr, cptab, cpt, sizeof(*(ptr)))
>> 
>> -# define __OBD_VMALLOC_VEROBSE(ptr, cptab, cpt, size)			      \
>> +/* Direct use of __vmalloc_node() allows for protection flag specification
>> + * (and particularly to not set __GFP_FS, which is likely to cause some
>> + * deadlock situations in our code).
>> + */
>> +# define __OBD_VMALLOC_VERBOSE(ptr, cptab, cpt, size)			      \
>> do {									      \
>> -	(ptr) = cptab == NULL ?						      \
>> -		vzalloc(size) :						      \
>> -		vzalloc_node(size, cfs_cpt_spread_node(cptab, cpt));	      \
>> +	(ptr) = __vmalloc_node(size, 1, GFP_NOFS | __GFP_HIGHMEM | __GFP_ZERO,\
>> +			       PAGE_KERNEL,				      \
>> +			       cptab == NULL ? NUMA_NO_NODE :		      \
>> +					      cfs_cpt_spread_node(cptab, cpt),\
>> +			       __builtin_return_address(0));		      \
>> 	if (unlikely((ptr) == NULL)) {					\
>> 		CERROR("vmalloc of '" #ptr "' (%d bytes) failed\n",	   \
>> 		       (int)(size));					  \
>> @@ -671,9 +677,9 @@ do {									      \
>> } while (0)
>> 
>> # define OBD_VMALLOC(ptr, size)						      \
>> -	 __OBD_VMALLOC_VEROBSE(ptr, NULL, 0, size)
>> +	 __OBD_VMALLOC_VERBOSE(ptr, NULL, 0, size)
>> # define OBD_CPT_VMALLOC(ptr, cptab, cpt, size)				      \
>> -	 __OBD_VMALLOC_VEROBSE(ptr, cptab, cpt, size)
>> +	 __OBD_VMALLOC_VERBOSE(ptr, cptab, cpt, size)
>> 
>> 
>> /* Allocations above this size are considered too big and could not be done

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