Under shmem swapping and swapoff load, I sometimes hit the VM_BUG_ON_PAGE(!page->mapping) in mem_cgroup_commit_charge() at mm/memcontrol.c:6502! Each time it has been a call from shmem_unuse().
Yes, there are some cases (most commonly when the page being unswapped is in a file being unlinked and evicted at that time) when the charge should not be committed. In the old scheme, the page got uncharged again on release; but in the new scheme, it hits that BUG beforehand. It's a useful BUG, so adapt shmem_unuse() to allow for it. Which needs more info from shmem_unuse_inode(): so abuse -EAGAIN internally to replace the previous !found state (-ENOENT would be a more natural code, but that's exactly what you get when the swap has been evicted). Signed-off-by: Hugh Dickins <[email protected]> --- mm/shmem.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) --- 3.16-rc2-mm1/mm/shmem.c 2014-06-25 18:43:59.868588121 -0700 +++ linux/mm/shmem.c 2014-06-30 15:05:50.736335600 -0700 @@ -611,7 +611,7 @@ static int shmem_unuse_inode(struct shme radswap = swp_to_radix_entry(swap); index = radix_tree_locate_item(&mapping->page_tree, radswap); if (index == -1) - return 0; + return -EAGAIN; /* * Move _head_ to start search for next from here. @@ -670,7 +670,6 @@ static int shmem_unuse_inode(struct shme spin_unlock(&info->lock); swap_free(swap); } - error = 1; /* not an error, but entry was found */ } return error; } @@ -683,7 +682,6 @@ int shmem_unuse(swp_entry_t swap, struct struct list_head *this, *next; struct shmem_inode_info *info; struct mem_cgroup *memcg; - int found = 0; int error = 0; /* @@ -702,22 +700,24 @@ int shmem_unuse(swp_entry_t swap, struct if (error) goto out; /* No radix_tree_preload: swap entry keeps a place for page in tree */ + error = -EAGAIN; mutex_lock(&shmem_swaplist_mutex); list_for_each_safe(this, next, &shmem_swaplist) { info = list_entry(this, struct shmem_inode_info, swaplist); if (info->swapped) - found = shmem_unuse_inode(info, swap, &page); + error = shmem_unuse_inode(info, swap, &page); else list_del_init(&info->swaplist); cond_resched(); - if (found) + if (error != -EAGAIN) break; } mutex_unlock(&shmem_swaplist_mutex); - if (found < 0) { - error = found; + if (error) { + if (error != -ENOMEM) + error = 0; mem_cgroup_cancel_charge(page, memcg); } else mem_cgroup_commit_charge(page, memcg, true); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
