* Query - Related to kernel changes for GFP_NOIO flag
@ 2017-03-05 9:07 Suraj Choudhari
2017-03-05 9:10 ` Fwd: " Suraj Choudhari
0 siblings, 1 reply; 2+ messages in thread
From: Suraj Choudhari @ 2017-03-05 9:07 UTC (permalink / raw)
To: linux-newbie
Hi,
The GFP_NOIO flag used for kmalloc is currently defined to be '__GFP_RECLAIM'
#define GFP_NOIO (__GFP_RECLAIM)
#define __GFP_RECLAIM ((__force
gfp_t)(___GFP_DIRECT_RECLAIM|___GFP_KSWAPD_RECLAIM
However, prior to 4.4 kernel, this flag was defined as __GFP_WAIT.
#define GFP_NOIO (__GFP_WAIT)
Queries -
======
1] Can any physical disk IO happen due to memory allocation done
using 'GFP_NOIO' ?
The reason to ask is since the GFP_NOIO is now modified to use
__GFP_KSWAPD_RECLAIM, so I am thinking that physical disk IO may
probably happen whiel swapping the stale pages to disk in kswapd.
2] If kernel code wants to use kmalloc() and wants to ensure there is
NO any physical/disk IO due to kmalloc, shall the kernel code use
__GFP_DIRECT_RECLAIM instead of GFP_NOIO ?
Thanks,
Suraj
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^ permalink raw reply [flat|nested] 2+ messages in thread
* Fwd: Query - Related to kernel changes for GFP_NOIO flag
2017-03-05 9:07 Query - Related to kernel changes for GFP_NOIO flag Suraj Choudhari
@ 2017-03-05 9:10 ` Suraj Choudhari
0 siblings, 0 replies; 2+ messages in thread
From: Suraj Choudhari @ 2017-03-05 9:10 UTC (permalink / raw)
To: linux-kernel
Hi,
GFP_NOIO flag used for kmalloc is currently defined as - '__GFP_RECLAIM'
#define GFP_NOIO (__GFP_RECLAIM)
#define __GFP_RECLAIM ((__force
gfp_t)(___GFP_DIRECT_RECLAIM|___GFP_KSWAPD_RECLAIM
However, prior to 4.4 kernel, this flag was defined as __GFP_WAIT.
#define GFP_NOIO (__GFP_WAIT)
Queries -
======
1] Can any physical disk IO happen due to memory allocation done
using 'GFP_NOIO' ?
The reason to ask is since the GFP_NOIO is now modified to use
__GFP_KSWAPD_RECLAIM, so I am thinking that physical disk IO may
probably happen while swapping the stale pages to disk in kswapd.
2] If kernel code wants to use kmalloc() and wants to ensure there is
NO any physical/disk IO due to kmalloc, shall the kernel code use
__GFP_DIRECT_RECLAIM instead of GFP_NOIO ?
Thanks,
Suraj
^ permalink raw reply [flat|nested] 2+ messages in thread
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