On Sun, Jan 28, 2024 at 04:45:32PM +0100, Michal Hocko wrote:
> On Fri 26-01-24 17:07:56, Kent Overstreet wrote:
> > If we're using PF_MEMALLOC, we might have a fallback and might not to
> > warn about a failing allocation - thus we need a PF_* equivalent of
> > __GFP_NOWARN.
>
> Could you be more specific about the user? Is this an allocation from
> the reclaim path or an explicit PF_MEMALLOC one? It would be also really
> helpful to explain why GFP_NOWARN cannot be used directly.
Explicit PF_MEMALLOC.
It's for a call to alloc_inode(), which doesn't take gfp flags, and
plumbing it would require modifying a s_ops callback and would touch
every filesystem - but we want to get away from gfp flags anyways :)
More specifically, the code where I'm using it is doing a "try
GFP_NOWAIT first; if that fails drop locks and do GFP_KERNEL" dance;
it's part of a cleanup for some weird lifetime stuff related to
fs/inode.c.
#define memalloc_flags_do(_flags, _do) \
({ \
unsigned _saved_flags = memalloc_flags_save(_flags); \
typeof(_do) _ret = _do; \
memalloc_noreclaim_restore(_saved_flags); \
_ret; \
})
/*
* Allocate a new inode, dropping/retaking btree locks if necessary:
*/
static struct bch_inode_info *bch2_new_inode(struct btree_trans *trans)
{
struct bch_fs *c = trans->c;
struct bch_inode_info *inode =
memalloc_flags_do(PF_MEMALLOC|PF_MEMALLOC_NOWARN, to_bch_ei(new_inode(c->vfs_sb)));
if (unlikely(!inode)) {
int ret = drop_locks_do(trans, (inode = to_bch_ei(new_inode(c->vfs_sb))) ? 0 : -ENOMEM);
if (ret && inode)
discard_new_inode(&inode->v);
if (ret)
return ERR_PTR(ret);
}
return inode;
}
