Re: [Linaro-mm-sig] [PATCH v4 1/4] mm: cma: introduce gfp flag in cma_alloc instead of no_warn
On Tue, Jan 26, 2021 at 08:38:08AM +0100, Michal Hocko wrote:
On Mon 25-01-21 11:42:34, Minchan Kim wrote:
On Mon, Jan 25, 2021 at 02:07:01PM +0100, Michal Hocko wrote:
On Thu 21-01-21 09:54:59, Minchan Kim wrote:
The upcoming patch will introduce __GFP_NORETRY semantic in alloc_contig_range which is a failfast mode of the API. Instead of adding a additional parameter for gfp, replace no_warn with gfp flag.
To keep old behaviors, it follows the rule below.
no_warn gfp_flags
false GFP_KERNEL true GFP_KERNEL|__GFP_NOWARN gfp & __GFP_NOWARN GFP_KERNEL | (gfp & __GFP_NOWARN)
Reviewed-by: Suren Baghdasaryan surenb@google.com Signed-off-by: Minchan Kim minchan@kernel.org
[...]
diff --git a/mm/cma.c b/mm/cma.c index 0ba69cd16aeb..d50627686fec 100644 --- a/mm/cma.c +++ b/mm/cma.c @@ -419,13 +419,13 @@ static inline void cma_debug_show_areas(struct cma *cma) { }
- @cma: Contiguous memory region for which the allocation is performed.
- @count: Requested number of pages.
- @align: Requested alignment of pages (in PAGE_SIZE order).
- @no_warn: Avoid printing message about failed allocation
- @gfp_mask: GFP mask to use during the cma allocation.
Call out supported gfp flags explicitly. Have a look at kvmalloc_node for a guidance.
How about this?
diff --git a/mm/cma.c b/mm/cma.c index d50627686fec..b94727b694d6 100644 --- a/mm/cma.c +++ b/mm/cma.c @@ -423,6 +423,10 @@ static inline void cma_debug_show_areas(struct cma *cma) { }
- This function allocates part of contiguous memory on specific
- contiguous memory area.
- For gfp_mask, GFP_KERNEL and __GFP_NORETRY are supported. __GFP_NORETRY
- will avoid costly functions(e.g., waiting on page_writeback and locking)
- at current implementaion during the page migration.
rather than explicitly mentioning what the flag implies I think it would be more useful to state the intended usecase. See how kvmalloc_node says "__GFP_RETRY_MAYFAIL is supported, and it should be used only if kmalloc is preferable to the vmalloc fallback, due to visible performance drawbacks. __GFP_NOWARN is also supported to suppress allocation failure messages."
This would help people not familiar with internals to see whether this flag is a good fit for them.
In this case I woul go with " @flags: gfp mask. Must be compatible (superset) with GFP_KERNEL. [...] Reclaim modifiers (__GFP_RETRY_MAYFAIL, __GFP_NOFAIL) are not supported. __GFP_NORETRY is supported, and it should be used for opportunistic allocation attempts that should rather fail quickly when the caller has a fallback strategy. "
Obviously for this patch you will go with a simple statement that Reclaim modifiers are not supported at all.
After more discussion for gfp_flags in thread of next patch, let me changes a bit more based on it.
Thanks for the suggestion, Michal.
On Tue, Jan 26, 2021 at 11:12:14AM -0800, Minchan Kim wrote:
On Tue, Jan 26, 2021 at 08:38:08AM +0100, Michal Hocko wrote:
On Mon 25-01-21 11:42:34, Minchan Kim wrote:
On Mon, Jan 25, 2021 at 02:07:01PM +0100, Michal Hocko wrote:
On Thu 21-01-21 09:54:59, Minchan Kim wrote:
The upcoming patch will introduce __GFP_NORETRY semantic in alloc_contig_range which is a failfast mode of the API. Instead of adding a additional parameter for gfp, replace no_warn with gfp flag.
To keep old behaviors, it follows the rule below.
no_warn gfp_flags
false GFP_KERNEL true GFP_KERNEL|__GFP_NOWARN gfp & __GFP_NOWARN GFP_KERNEL | (gfp & __GFP_NOWARN)
Reviewed-by: Suren Baghdasaryan surenb@google.com Signed-off-by: Minchan Kim minchan@kernel.org
[...]
diff --git a/mm/cma.c b/mm/cma.c index 0ba69cd16aeb..d50627686fec 100644 --- a/mm/cma.c +++ b/mm/cma.c @@ -419,13 +419,13 @@ static inline void cma_debug_show_areas(struct cma *cma) { }
- @cma: Contiguous memory region for which the allocation is performed.
- @count: Requested number of pages.
- @align: Requested alignment of pages (in PAGE_SIZE order).
- @no_warn: Avoid printing message about failed allocation
- @gfp_mask: GFP mask to use during the cma allocation.
Call out supported gfp flags explicitly. Have a look at kvmalloc_node for a guidance.
How about this?
diff --git a/mm/cma.c b/mm/cma.c index d50627686fec..b94727b694d6 100644 --- a/mm/cma.c +++ b/mm/cma.c @@ -423,6 +423,10 @@ static inline void cma_debug_show_areas(struct cma *cma) { }
- This function allocates part of contiguous memory on specific
- contiguous memory area.
- For gfp_mask, GFP_KERNEL and __GFP_NORETRY are supported. __GFP_NORETRY
- will avoid costly functions(e.g., waiting on page_writeback and locking)
- at current implementaion during the page migration.
rather than explicitly mentioning what the flag implies I think it would be more useful to state the intended usecase. See how kvmalloc_node says "__GFP_RETRY_MAYFAIL is supported, and it should be used only if kmalloc is preferable to the vmalloc fallback, due to visible performance drawbacks. __GFP_NOWARN is also supported to suppress allocation failure messages."
This would help people not familiar with internals to see whether this flag is a good fit for them.
In this case I woul go with " @flags: gfp mask. Must be compatible (superset) with GFP_KERNEL. [...] Reclaim modifiers (__GFP_RETRY_MAYFAIL, __GFP_NOFAIL) are not supported. __GFP_NORETRY is supported, and it should be used for opportunistic allocation attempts that should rather fail quickly when the caller has a fallback strategy. "
Obviously for this patch you will go with a simple statement that Reclaim modifiers are not supported at all.
After more discussion for gfp_flags in thread of next patch, let me changes a bit more based on it.
Thanks for the suggestion, Michal.
Based on the discussion in other thread, I want to go with __GFP_NORETRY to indicate "opportunistic-easy-to-fail attempt" so suggestion words Michal is valid so I will carry it on next version.
Thank you.
linaro-mm-sig@lists.linaro.org
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Minchan Kim