On Tue 26-10-21 10:26:06, Neil Brown wrote: > On Tue, 26 Oct 2021, Michal Hocko wrote: > > From: Michal Hocko <mhocko@xxxxxxxx> > > > > The core of the vmalloc allocator __vmalloc_area_node doesn't say > > anything about gfp mask argument. Not all gfp flags are supported > > though. Be more explicit about constrains. > > > > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> > > --- > > mm/vmalloc.c | 12 ++++++++++-- > > 1 file changed, 10 insertions(+), 2 deletions(-) > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > index 602649919a9d..2199d821c981 100644 > > --- a/mm/vmalloc.c > > +++ b/mm/vmalloc.c > > @@ -2980,8 +2980,16 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask, > > * @caller: caller's return address > > * > > * Allocate enough pages to cover @size from the page level > > - * allocator with @gfp_mask flags. Map them into contiguous > > - * kernel virtual space, using a pagetable protection of @prot. > > + * allocator with @gfp_mask flags. Please note that the full set of gfp > > + * flags are not supported. GFP_KERNEL would be a preferred allocation mode > > + * but GFP_NOFS and GFP_NOIO are supported as well. Zone modifiers are not > > In what sense is GFP_KERNEL "preferred"?? > The choice of GFP_NOFS, when necessary, isn't based on preference but > on need. > > I understand that you would prefer no one ever used GFP_NOFs ever - just > use the scope API. I even agree. But this is not the place to make > that case. Any suggestion for a better wording? > > + * supported. From the reclaim modifiers__GFP_DIRECT_RECLAIM is required (aka > > + * GFP_NOWAIT is not supported) and only __GFP_NOFAIL is supported (aka > > I don't think "aka" is the right thing to use here. It is short for > "also known as" and there is nothing that is being known as something > else. > It would be appropriate to say (i.e. GFP_NOWAIT is not supported). > "i.e." is short for the Latin "id est" which means "that is" and > normally introduces an alternate description (whereas aka introduces an > alternate name). OK > > + * __GFP_NORETRY and __GFP_RETRY_MAYFAIL are not supported). > > Why do you think __GFP_NORETRY and __GFP_RETRY_MAYFAIL are not supported. Because they cannot be passed to the page table allocator. In both cases the allocation would fail when system is short on memory. GFP_KERNEL used for ptes implicitly doesn't behave that way. > > > + * __GFP_NOWARN can be used to suppress error messages about failures. > > Surely "NOWARN" suppresses warning messages, not error messages .... I am not sure I follow. NOWARN means "do not warn" independently on the log level chosen for the message. Is an allocation failure an error message? Is the "vmalloc error: size %lu, failed to map pages" an error message? Anyway I will go with "__GFP_NOWARN can be used to suppress failure messages" Is that better? -- Michal Hocko SUSE Labs
