Re: [PATCH v5 03/13] mm/shmem: Support memfile_notifier

[Vishal Annapurve <vannapurve@google.com>]

On Thu, Mar 10, 2022 at 6:10 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
>
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>
> It maintains a memfile_notifier list in shmem_inode_info structure and
> implements memfile_pfn_ops callbacks defined by memfile_notifier. It
> then exposes them to memfile_notifier via
> shmem_get_memfile_notifier_info.
>
> We use SGP_NOALLOC in shmem_get_lock_pfn since the pages should be
> allocated by userspace for private memory. If there is no pages
> allocated at the offset then error should be returned so KVM knows that
> the memory is not private memory.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
>  include/linux/shmem_fs.h |  4 +++
>  mm/shmem.c               | 76 ++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 80 insertions(+)
>
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> index 2dde843f28ef..7bb16f2d2825 100644
> --- a/include/linux/shmem_fs.h
> +++ b/include/linux/shmem_fs.h
> @@ -9,6 +9,7 @@
>  #include <linux/percpu_counter.h>
>  #include <linux/xattr.h>
>  #include <linux/fs_parser.h>
> +#include <linux/memfile_notifier.h>
>
>  /* inode in-kernel data */
>
> @@ -28,6 +29,9 @@ struct shmem_inode_info {
>         struct simple_xattrs    xattrs;         /* list of xattrs */
>         atomic_t                stop_eviction;  /* hold when working on inode */
>         unsigned int            xflags;         /* shmem extended flags */
> +#ifdef CONFIG_MEMFILE_NOTIFIER
> +       struct memfile_notifier_list memfile_notifiers;
> +#endif
>         struct inode            vfs_inode;
>  };
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 9b31a7056009..7b43e274c9a2 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -903,6 +903,28 @@ static struct folio *shmem_get_partial_folio(struct inode *inode, pgoff_t index)
>         return page ? page_folio(page) : NULL;
>  }
>
> +static void notify_fallocate(struct inode *inode, pgoff_t start, pgoff_t end)
> +{
> +#ifdef CONFIG_MEMFILE_NOTIFIER
> +       struct shmem_inode_info *info = SHMEM_I(inode);
> +
> +       memfile_notifier_fallocate(&info->memfile_notifiers, start, end);
> +#endif
> +}
> +
> +static void notify_invalidate_page(struct inode *inode, struct folio *folio,
> +                                  pgoff_t start, pgoff_t end)
> +{
> +#ifdef CONFIG_MEMFILE_NOTIFIER
> +       struct shmem_inode_info *info = SHMEM_I(inode);
> +
> +       start = max(start, folio->index);
> +       end = min(end, folio->index + folio_nr_pages(folio));
> +
> +       memfile_notifier_invalidate(&info->memfile_notifiers, start, end);
> +#endif
> +}
> +
>  /*
>   * Remove range of pages and swap entries from page cache, and free them.
>   * If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate.
> @@ -946,6 +968,8 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
>                         }
>                         index += folio_nr_pages(folio) - 1;
>
> +                       notify_invalidate_page(inode, folio, start, end);
> +
>                         if (!unfalloc || !folio_test_uptodate(folio))
>                                 truncate_inode_folio(mapping, folio);
>                         folio_unlock(folio);
> @@ -1019,6 +1043,9 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
>                                         index--;
>                                         break;
>                                 }
> +
> +                               notify_invalidate_page(inode, folio, start, end);
> +

Should this be done in batches or done once for all of range [start, end)?

>                                 VM_BUG_ON_FOLIO(folio_test_writeback(folio),
>                                                 folio);
>                                 truncate_inode_folio(mapping, folio);
> @@ -2279,6 +2306,9 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
>                 info->flags = flags & VM_NORESERVE;
>                 INIT_LIST_HEAD(&info->shrinklist);
>                 INIT_LIST_HEAD(&info->swaplist);
> +#ifdef CONFIG_MEMFILE_NOTIFIER
> +               memfile_notifier_list_init(&info->memfile_notifiers);
> +#endif
>                 simple_xattrs_init(&info->xattrs);
>                 cache_no_acl(inode);
>                 mapping_set_large_folios(inode->i_mapping);
> @@ -2802,6 +2832,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
>         if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size)
>                 i_size_write(inode, offset + len);
>         inode->i_ctime = current_time(inode);
> +       notify_fallocate(inode, start, end);
>  undone:
>         spin_lock(&inode->i_lock);
>         inode->i_private = NULL;
> @@ -3909,6 +3940,47 @@ static struct file_system_type shmem_fs_type = {
>         .fs_flags       = FS_USERNS_MOUNT,
>  };
>
> +#ifdef CONFIG_MEMFILE_NOTIFIER
> +static long shmem_get_lock_pfn(struct inode *inode, pgoff_t offset, int *order)
> +{
> +       struct page *page;
> +       int ret;
> +
> +       ret = shmem_getpage(inode, offset, &page, SGP_NOALLOC);
> +       if (ret)
> +               return ret;
> +
> +       *order = thp_order(compound_head(page));
> +
> +       return page_to_pfn(page);
> +}
> +
> +static void shmem_put_unlock_pfn(unsigned long pfn)
> +{
> +       struct page *page = pfn_to_page(pfn);
> +
> +       VM_BUG_ON_PAGE(!PageLocked(page), page);
> +
> +       set_page_dirty(page);
> +       unlock_page(page);
> +       put_page(page);
> +}
> +
> +static struct memfile_notifier_list* shmem_get_notifier_list(struct inode *inode)
> +{
> +       if (!shmem_mapping(inode->i_mapping))
> +               return NULL;
> +
> +       return  &SHMEM_I(inode)->memfile_notifiers;
> +}
> +
> +static struct memfile_backing_store shmem_backing_store = {
> +       .pfn_ops.get_lock_pfn = shmem_get_lock_pfn,
> +       .pfn_ops.put_unlock_pfn = shmem_put_unlock_pfn,
> +       .get_notifier_list = shmem_get_notifier_list,
> +};
> +#endif /* CONFIG_MEMFILE_NOTIFIER */
> +
>  int __init shmem_init(void)
>  {
>         int error;
> @@ -3934,6 +4006,10 @@ int __init shmem_init(void)
>         else
>                 shmem_huge = SHMEM_HUGE_NEVER; /* just in case it was patched */
>  #endif
> +
> +#ifdef CONFIG_MEMFILE_NOTIFIER
> +       memfile_register_backing_store(&shmem_backing_store);
> +#endif
>         return 0;
>
>  out1:
> --
> 2.17.1
>