On Mon, 13 Jul 2020 20:41:11 -0700 Eric Biggers wrote: > On Tue, Jul 14, 2020 at 11:32:52AM +0800, Hillf Danton wrote: > > > > Add FALLOC_FL_NOBLOCK and on the shmem side try to lock inode upon the > > new flag. And the overall upside is to keep the current gfp either in > > the khugepaged context or not. > > > > --- a/include/uapi/linux/falloc.h > > +++ b/include/uapi/linux/falloc.h > > @@ -77,4 +77,6 @@ > > */ > > #define FALLOC_FL_UNSHARE_RANGE 0x40 > > > > +#define FALLOC_FL_NOBLOCK 0x80 > > + > > You can't add a new UAPI flag to fix a kernel-internal problem like this.
Sounds fair, see below. What the report indicates is a missing PF_MEMALLOC_NOFS and it's checked on the ashmem side and added as an exception before going to filesystem. On shmem side, no more than a best effort is paid on the inteded exception. --- a/drivers/staging/android/ashmem.c +++ b/drivers/staging/android/ashmem.c @@ -437,6 +437,7 @@ static unsigned long ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) { unsigned long freed = 0; + bool nofs; /* We might recurse into filesystem code, so bail out if necessary */ if (!(sc->gfp_mask & __GFP_FS)) @@ -445,6 +446,11 @@ ashmem_shrink_scan(struct shrinker *shri if (!mutex_trylock(&ashmem_mutex)) return -1; + /* enter filesystem with caution: nonblock on locking */ + nofs = current->flags & PF_MEMALLOC_NOFS; + if (!nofs) + current->flags |= PF_MEMALLOC_NOFS; + while (!list_empty(&ashmem_lru_list)) { struct ashmem_range *range = list_first_entry(&ashmem_lru_list, typeof(*range), lru); @@ -472,6 +478,8 @@ ashmem_shrink_scan(struct shrinker *shri } mutex_unlock(&ashmem_mutex); out: + if (!nofs) + current->flags &= ~PF_MEMALLOC_NOFS; return freed; } --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2728,7 +2728,12 @@ static long shmem_fallocate(struct file if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE)) return -EOPNOTSUPP; - inode_lock(inode); + if (current->flags & PF_MEMALLOC_NOFS) { + /* this exception needs a best effort and no more */ + if (!inode_trylock(inode)) + return -EBUSY; + } else + inode_lock(inode); if (mode & FALLOC_FL_PUNCH_HOLE) { struct address_space *mapping = file->f_mapping; _______________________________________________ devel mailing list de...@linuxdriverproject.org http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel