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

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