On Fri, Jun 21, 2019 at 01:10:54PM +0000, Song Liu wrote:
>
>
> > On Jun 21, 2019, at 6:07 AM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote:
> >
> > On Thu, Jun 20, 2019 at 01:53:48PM -0700, Song Liu wrote:
> >> In previous patch, an application could put part of its text section in
> >> THP via madvise(). These THPs will be protected from writes when the
> >> application is still running (TXTBSY). However, after the application
> >> exits, the file is available for writes.
> >>
> >> This patch avoids writes to file THP by dropping page cache for the file
> >> when the file is open for write. A new counter nr_thps is added to struct
> >> address_space. In do_last(), if the file is open for write and nr_thps
> >> is non-zero, we drop page cache for the whole file.
> >>
> >> Signed-off-by: Song Liu <songliubraving@xxxxxx>
> >> ---
> >> fs/inode.c | 3 +++
> >> fs/namei.c | 22 +++++++++++++++++++++-
> >> include/linux/fs.h | 31 +++++++++++++++++++++++++++++++
> >> mm/filemap.c | 1 +
> >> mm/khugepaged.c | 4 +++-
> >> 5 files changed, 59 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/fs/inode.c b/fs/inode.c
> >> index df6542ec3b88..518113a4e219 100644
> >> --- a/fs/inode.c
> >> +++ b/fs/inode.c
> >> @@ -181,6 +181,9 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
> >> mapping->flags = 0;
> >> mapping->wb_err = 0;
> >> atomic_set(&mapping->i_mmap_writable, 0);
> >> +#ifdef CONFIG_READ_ONLY_THP_FOR_FS
> >> + atomic_set(&mapping->nr_thps, 0);
> >> +#endif
> >> mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);
> >> mapping->private_data = NULL;
> >> mapping->writeback_index = 0;
> >> diff --git a/fs/namei.c b/fs/namei.c
> >> index 20831c2fbb34..de64f24b58e9 100644
> >> --- a/fs/namei.c
> >> +++ b/fs/namei.c
> >> @@ -3249,6 +3249,22 @@ static int lookup_open(struct nameidata *nd, struct path *path,
> >> return error;
> >> }
> >>
> >> +/*
> >> + * The file is open for write, so it is not mmapped with VM_DENYWRITE. If
> >> + * it still has THP in page cache, drop the whole file from pagecache
> >> + * before processing writes. This helps us avoid handling write back of
> >> + * THP for now.
> >> + */
> >> +static inline void release_file_thp(struct file *file)
> >> +{
> >> +#ifdef CONFIG_READ_ONLY_THP_FOR_FS
> >> + struct inode *inode = file_inode(file);
> >> +
> >> + if (inode_is_open_for_write(inode) && filemap_nr_thps(inode->i_mapping))
> >> + truncate_pagecache(inode, 0);
> >> +#endif
> >> +}
> >> +
> >> /*
> >> * Handle the last step of open()
> >> */
> >> @@ -3418,7 +3434,11 @@ static int do_last(struct nameidata *nd,
> >> goto out;
> >> opened:
> >> error = ima_file_check(file, op->acc_mode);
> >> - if (!error && will_truncate)
> >> + if (error)
> >> + goto out;
> >> +
> >> + release_file_thp(file);
> >
> > What protects against re-fill the file with THP in parallel?
>
> khugepaged would only process vma with VM_DENYWRITE. So once the
> file is open for write (i_write_count > 0), khugepage will not
> collapse the pages.
I have not look at the patch very closely. Do you only create THP by
khugepaged? Not in fault path?
--
Kirill A. Shutemov
