[Virtio-fs] [PATCH] virtiofs: FUSE_REMOVEMAPPING remove multiple entries in one call

[Liu Bo]

On Wed, Jun 05, 2019 at 02:35:14PM -0400, Vivek Goyal wrote:
> On Wed, Jun 05, 2019 at 11:06:46AM -0700, Liu Bo wrote:
> 
> [..]
> > > -/*
> > > - * It is called from evict_inode() and by that time inode is going away. So
> > > - * this function does not take any locks like fi->i_dmap_sem for traversing
> > > - * that fuse inode interval tree. If that lock is taken then lock validator
> > > - * complains of deadlock situation w.r.t fs_reclaim lock.
> > > - */
> > > -void fuse_removemapping(struct inode *inode)
> > > +static int dmap_list_send_removemappings(struct inode *inode, unsigned num,
> > > +					 struct list_head *to_remove)
> > >  {
> > > -	struct fuse_conn *fc = get_fuse_conn(inode);
> > > -	struct fuse_inode *fi = get_fuse_inode(inode);
> > > -	ssize_t err;
> > > +	struct fuse_removemapping_one *remove_one, *ptr;
> > > +	struct fuse_removemapping_in inarg;
> > >  	struct fuse_dax_mapping *dmap;
> > > +	int ret, i = 0, nr_alloc;
> > >  
> > > -	/* Clear the mappings list */
> > > -	while (true) {
> > > -		WARN_ON(fi->nr_dmaps < 0);
> > > +	nr_alloc = min_t(unsigned int, num, FUSE_REMOVEMAPPING_MAX_ENTRY);
> > > +	remove_one = kmalloc_array(nr_alloc, sizeof(*remove_one), GFP_NOIO);
> > 
> > GFP_NOIO's comments implies that memalloc_noio_{save,restore} are preferred,
> > also would GFP_NOFS be better?
> 
> GFP_NOFS sounds reasonable. I am not sure how memalloc_noio_{save,restore}
> API is better as opposed to using GFP_NOFS.
>

mm devs need memalloc_nofs_{save,restore} to encourage fs to declare a
scope that all children callees inherit the nofs attribute.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7dea19f9ee636cb244109a4dba426bbb3e5304b7

thanks,
-liubo

> [..]
> > > +/*
> > > + * Cleanup dmap entry and add back to free list. This should be called with
> > > + * fc->lock held.
> > > + */
> > > +static void fuse_dax_do_free_mapping_locked(struct fuse_conn *fc,
> > > +					    struct fuse_dax_mapping *dmap)
> > > +{
> > > +	__dmap_remove_busy_list(fc, dmap);
> > > +	dmap->inode = NULL;
> > > +	dmap->start = dmap->end = 0;
> > > +	__free_dax_mapping(fc, dmap);
> > > +	pr_debug("fuse: freed memory range start=0x%llx end=0x%llx "
> > > +		"window_offset=0x%llx length=0x%llx\n", dmap->start,
> > > +		dmap->end, dmap->window_offset, dmap->length);
> > 
> > pr_debug() needs to be placed at the beginning as dmap->start & end have been
> > zero'd.
> > 
> 
> Good point. Will fix.
> 
> Vivek