On Fri, Mar 31, 2017 at 8:30 AM, Andrey Ryabinin <[email protected]> wrote: > zswap_frontswap_store() is called during memory reclaim from > __frontswap_store() from swap_writepage() from shrink_page_list(). > This may happen in NOFS context, thus zswap shouldn't use __GFP_FS, > otherwise we may renter into fs code and deadlock. > zswap_frontswap_store() also shouldn't use __GFP_IO to avoid recursion > into itself. >
Is it possible to enter fs code (or IO) from zswap_frontswap_store() other than recursive memory reclaim? However recursive memory reclaim is protected through PF_MEMALLOC task flag. The change seems fine but IMHO reasoning needs an update. Adding Michal for expert opinion. > zswap_frontswap_store() call zpool_malloc() with __GFP_NORETRY | > __GFP_NOWARN | __GFP_KSWAPD_RECLAIM, so let's use the same flags for > zswap_entry_cache_alloc() as well, instead of GFP_KERNEL. > > Signed-off-by: Andrey Ryabinin <[email protected]> > --- > mm/zswap.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/mm/zswap.c b/mm/zswap.c > index eedc278..12ad7e9 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -966,6 +966,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t > offset, > struct zswap_tree *tree = zswap_trees[type]; > struct zswap_entry *entry, *dupentry; > struct crypto_comp *tfm; > + gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM; > int ret; > unsigned int dlen = PAGE_SIZE, len; > unsigned long handle; > @@ -989,7 +990,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t > offset, > } > > /* allocate entry */ > - entry = zswap_entry_cache_alloc(GFP_KERNEL); > + entry = zswap_entry_cache_alloc(gfp); > if (!entry) { > zswap_reject_kmemcache_fail++; > ret = -ENOMEM; > @@ -1017,9 +1018,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t > offset, > > /* store */ > len = dlen + sizeof(struct zswap_header); > - ret = zpool_malloc(entry->pool->zpool, len, > - __GFP_NORETRY | __GFP_NOWARN | > __GFP_KSWAPD_RECLAIM, > - &handle); > + ret = zpool_malloc(entry->pool->zpool, len, gfp, &handle); > if (ret == -ENOSPC) { > zswap_reject_compress_poor++; > goto put_dstmem; > -- > 2.10.2 >
