On Tue, 26 Oct 2021, Michal Hocko wrote:
> On Tue 26-10-21 10:34:34, Neil Brown wrote:
> > On Tue, 26 Oct 2021, Michal Hocko wrote:
> > > From: Michal Hocko <mhocko@xxxxxxxx>
> > >
> > > A support for GFP_NO{FS,IO} and __GFP_NOFAIL has been implemented
> > > by previous patches so we can allow the support for kvmalloc. This
> > > will allow some external users to simplify or completely remove
> > > their helpers.
> > >
> > > GFP_NOWAIT semantic hasn't been supported so far but it hasn't been
> > > explicitly documented so let's add a note about that.
> > >
> > > ceph_kvmalloc is the first helper to be dropped and changed to
> > > kvmalloc.
> > >
> > > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> > > ---
> > > include/linux/ceph/libceph.h | 1 -
> > > mm/util.c | 15 ++++-----------
> > > net/ceph/buffer.c | 4 ++--
> > > net/ceph/ceph_common.c | 27 ---------------------------
> > > net/ceph/crypto.c | 2 +-
> > > net/ceph/messenger.c | 2 +-
> > > net/ceph/messenger_v2.c | 2 +-
> > > net/ceph/osdmap.c | 12 ++++++------
> > > 8 files changed, 15 insertions(+), 50 deletions(-)
> > >
> > > diff --git a/include/linux/ceph/libceph.h b/include/linux/ceph/libceph.h
> > > index 409d8c29bc4f..309acbcb5a8a 100644
> > > --- a/include/linux/ceph/libceph.h
> > > +++ b/include/linux/ceph/libceph.h
> > > @@ -295,7 +295,6 @@ extern bool libceph_compatible(void *data);
> > >
> > > extern const char *ceph_msg_type_name(int type);
> > > extern int ceph_check_fsid(struct ceph_client *client, struct ceph_fsid *fsid);
> > > -extern void *ceph_kvmalloc(size_t size, gfp_t flags);
> > >
> > > struct fs_parameter;
> > > struct fc_log;
> > > diff --git a/mm/util.c b/mm/util.c
> > > index bacabe446906..fdec6b4b1267 100644
> > > --- a/mm/util.c
> > > +++ b/mm/util.c
> > > @@ -549,13 +549,10 @@ EXPORT_SYMBOL(vm_mmap);
> > > * Uses kmalloc to get the memory but if the allocation fails then falls back
> > > * to the vmalloc allocator. Use kvfree for freeing the memory.
> > > *
> > > - * Reclaim modifiers - __GFP_NORETRY and __GFP_NOFAIL are not supported.
> > > + * Reclaim modifiers - __GFP_NORETRY and GFP_NOWAIT are not supported.
> >
> > GFP_NOWAIT is not a modifier. It is a base value that can be modified.
> > I think you mean that
> > __GFP_NORETRY is not supported and __GFP_DIRECT_RECLAIM is required
>
> I thought naming the higher level gfp mask would be more helpful here.
> Most people do not tend to think in terms of __GFP_DIRECT_RECLAIM but
> rather GFP_NOWAIT or GFP_ATOMIC.
Maybe it would. But the text says "Reclaim modifiers" and then lists
one modifier and one mask. That is confusing.
If you want to mention both, keep them separate.
GFP_NOWAIT and GFP_ATOMIC are not supported, neither is the
__GFP_NORETRY modifier.
or something like that.
Thanks,
NeilBrown
>
> > But I really cannot see why either of these statements are true.
>
> The reason is same as why vmalloc do not support neither of them.
>
> > Before your patch, __GFP_NORETRY would have forced use of kmalloc, so
> > that would mean it isn't really supported. But that doesn't happen any more.
>
> __GFP_NORETRY is used internaly by kvmalloc but that doesn't mean it is
> supported by the caller. In fact __GFP_NORETRY is used to implement a
> higher level logic of the prioritization between kmalloc and vmalloc
> fallback because some users would rather see vmalloc fallback even for
> smaller allocations which do not really fail otherwise (e.g. < order-4).
> --
> Michal Hocko
> SUSE Labs
>
>
