From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f197.google.com (mail-pl1-f197.google.com [209.85.214.197]) by kanga.kvack.org (Postfix) with ESMTP id 9A7846B774A for ; Wed, 5 Dec 2018 20:14:19 -0500 (EST) Received: by mail-pl1-f197.google.com with SMTP id ay11so16151130plb.20 for ; Wed, 05 Dec 2018 17:14:19 -0800 (PST) Received: from huawei.com (szxga07-in.huawei.com. [45.249.212.35]) by mx.google.com with ESMTPS id g31si21840173pld.358.2018.12.05.17.14.18 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 05 Dec 2018 17:14:18 -0800 (PST) Subject: Re: [PATCH] squashfs: enable __GFP_FS in ->readpage to prevent hang in mem alloc From: Hou Tao References: <20181204020840.49576-1-houtao1@huawei.com> Message-ID: <4315acd7-f4b2-b11d-18d8-ab6ce63244b3@huawei.com> Date: Thu, 6 Dec 2018 09:14:13 +0800 MIME-Version: 1.0 In-Reply-To: <20181204020840.49576-1-houtao1@huawei.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: phillip@squashfs.org.uk Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org ping ? On 2018/12/4 10:08, Hou Tao wrote: > There is no need to disable __GFP_FS in ->readpage: > * It's a read-only fs, so there will be no dirty/writeback page and > there will be no deadlock against the caller's locked page > * It just allocates one page, so compaction will not be invoked > * It doesn't take any inode lock, so the reclamation of inode will be fine > > And no __GFP_FS may lead to hang in __alloc_pages_slowpath() if a > squashfs page fault occurs in the context of a memory hogger, because > the hogger will not be killed due to the logic in __alloc_pages_may_oom(). > > Signed-off-by: Hou Tao > --- > fs/squashfs/file.c | 3 ++- > fs/squashfs/file_direct.c | 4 +++- > fs/squashfs/squashfs_fs_f.h | 25 +++++++++++++++++++++++++ > 3 files changed, 30 insertions(+), 2 deletions(-) > create mode 100644 fs/squashfs/squashfs_fs_f.h > > diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c > index f1c1430ae721..8603dda4a719 100644 > --- a/fs/squashfs/file.c > +++ b/fs/squashfs/file.c > @@ -51,6 +51,7 @@ > #include "squashfs_fs.h" > #include "squashfs_fs_sb.h" > #include "squashfs_fs_i.h" > +#include "squashfs_fs_f.h" > #include "squashfs.h" > > /* > @@ -414,7 +415,7 @@ void squashfs_copy_cache(struct page *page, struct squashfs_cache_entry *buffer, > TRACE("bytes %d, i %d, available_bytes %d\n", bytes, i, avail); > > push_page = (i == page->index) ? page : > - grab_cache_page_nowait(page->mapping, i); > + squashfs_grab_cache_page_nowait(page->mapping, i); > > if (!push_page) > continue; > diff --git a/fs/squashfs/file_direct.c b/fs/squashfs/file_direct.c > index 80db1b86a27c..a0fdd6215348 100644 > --- a/fs/squashfs/file_direct.c > +++ b/fs/squashfs/file_direct.c > @@ -17,6 +17,7 @@ > #include "squashfs_fs.h" > #include "squashfs_fs_sb.h" > #include "squashfs_fs_i.h" > +#include "squashfs_fs_f.h" > #include "squashfs.h" > #include "page_actor.h" > > @@ -60,7 +61,8 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize, > /* Try to grab all the pages covered by the Squashfs block */ > for (missing_pages = 0, i = 0, n = start_index; i < pages; i++, n++) { > page[i] = (n == target_page->index) ? target_page : > - grab_cache_page_nowait(target_page->mapping, n); > + squashfs_grab_cache_page_nowait( > + target_page->mapping, n); > > if (page[i] == NULL) { > missing_pages++; > diff --git a/fs/squashfs/squashfs_fs_f.h b/fs/squashfs/squashfs_fs_f.h > new file mode 100644 > index 000000000000..fc5fb7aeb27d > --- /dev/null > +++ b/fs/squashfs/squashfs_fs_f.h > @@ -0,0 +1,25 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef SQUASHFS_FS_F > +#define SQUASHFS_FS_F > + > +/* > + * No need to use FGP_NOFS here: > + * 1. It's a read-only fs, so there will be no dirty/writeback page and > + * there will be no deadlock against the caller's locked page. > + * 2. It just allocates one page, so compaction will not be invoked. > + * 3. It doesn't take any inode lock, so the reclamation of inode > + * will be fine. > + * > + * And GFP_NOFS may lead to infinite loop in __alloc_pages_slowpath() if a > + * squashfs page fault occurs in the context of a memory hogger, because > + * the hogger will not be killed due to the logic in __alloc_pages_may_oom(). > + */ > +static inline struct page * > +squashfs_grab_cache_page_nowait(struct address_space *mapping, pgoff_t index) > +{ > + return pagecache_get_page(mapping, index, > + FGP_LOCK|FGP_CREAT|FGP_NOWAIT, > + mapping_gfp_mask(mapping)); > +} > +#endif > + >