From: Michal Hocko <mhocko@suse.com>
To: NeilBrown <neilb@suse.de>
Cc: linux-mm@kvack.org, Dave Chinner <david@fromorbit.com>,
Andrew Morton <akpm@linux-foundation.org>,
Christoph Hellwig <hch@infradead.org>,
Uladzislau Rezki <urezki@gmail.com>,
linux-fsdevel@vger.kernel.org,
LKML <linux-kernel@vger.kernel.org>,
Ilya Dryomov <idryomov@gmail.com>,
Jeff Layton <jlayton@kernel.org>
Subject: Re: [PATCH 3/4] mm/vmalloc: be more explicit about supported gfp flags.
Date: Tue, 26 Oct 2021 09:10:13 +0200 [thread overview]
Message-ID: <YXep1ctN1wPP+1a8@dhcp22.suse.cz> (raw)
In-Reply-To: <163520436674.16092.18372437960890952300@noble.neil.brown.name>
On Tue 26-10-21 10:26:06, Neil Brown wrote:
> On Tue, 26 Oct 2021, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@suse.com>
> >
> > 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@suse.com>
> > ---
> > 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
next prev parent reply other threads:[~2021-10-26 7:10 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-25 15:02 [PATCH 0/4] extend vmalloc support for constrained allocations Michal Hocko
2021-10-25 15:02 ` [PATCH 1/4] mm/vmalloc: alloc GFP_NO{FS,IO} for vmalloc Michal Hocko
2021-10-25 15:02 ` [PATCH 2/4] mm/vmalloc: add support for __GFP_NOFAIL Michal Hocko
2021-10-25 22:59 ` NeilBrown
2021-10-26 7:03 ` Michal Hocko
2021-10-26 10:30 ` NeilBrown
2021-10-26 11:29 ` Michal Hocko
2021-10-26 15:48 ` Uladzislau Rezki
2021-10-26 16:28 ` Michal Hocko
2021-10-26 19:33 ` Uladzislau Rezki
2021-10-27 6:46 ` Michal Hocko
2021-10-27 17:55 ` Uladzislau Rezki
2021-10-29 7:57 ` Michal Hocko
2021-10-29 14:05 ` Uladzislau Rezki
2021-10-29 14:45 ` Michal Hocko
2021-10-29 17:23 ` Uladzislau Rezki
2021-10-25 15:02 ` [PATCH 3/4] mm/vmalloc: be more explicit about supported gfp flags Michal Hocko
2021-10-25 23:26 ` NeilBrown
2021-10-26 7:10 ` Michal Hocko [this message]
2021-10-26 10:43 ` NeilBrown
2021-10-26 12:20 ` Michal Hocko
2021-10-25 15:02 ` [PATCH 4/4] mm: allow !GFP_KERNEL allocations for kvmalloc Michal Hocko
2021-10-25 23:34 ` NeilBrown
2021-10-26 7:15 ` Michal Hocko
2021-10-26 10:48 ` NeilBrown
2021-10-26 12:23 ` Michal Hocko
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