> 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.
Thanks,
Song
