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

[Chao Peng <chao.p.peng@linux.intel.com>]

On Tue, Apr 19, 2022 at 03:40:09PM -0700, Vishal Annapurve wrote:
> 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)?

Batching is definitely prefered. Will look at that.

Thanks,
Chao
> 
> >                                 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
> >