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 <houtao1@xxxxxxxxxx>
> ---
> 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
> +
>
