On Tue, 26 Oct 2021, Michal Hocko wrote: > 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? "GFP_KERNEL, GFP_NOFS, and GFP_NOIO are all supported". > > > > + * 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. Could you please point me to the particular allocation which uses GFP_KERNEL rather than the flags passed to __vmalloc_node()? I cannot find it. > > > > > > + * __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? If guess working with a C compiler has trained me to think that "warnings" are different from "errors". > > Anyway I will go with "__GFP_NOWARN can be used to suppress failure messages" > > Is that better? Yes, that's an excellent solution! Thanks. NeilBrown > -- > Michal Hocko > SUSE Labs > >
