On Thu, 2024-08-29 at 22:52 -0700, Darrick J. Wong wrote:
> On Thu, Aug 29, 2024 at 11:54:15PM -0400, Rik van Riel wrote:
> >
> > @@ -196,7 +196,7 @@ xfile_store(
> > unsigned int len;
> > unsigned int offset;
> >
> > - if (shmem_get_folio(inode, pos >> PAGE_SHIFT,
> > &folio,
> > + if (shmem_get_folio(inode, pos >> PAGE_SHIFT, 0,
> > &folio,
>
> Technically speaking, the "0" here could be (pos + count), though for
> the current xfile users this isn't likely to make much difference
> because online fsck's index building only appends small amounts of
> data
> (i.e. not larger than a PAGE_SIZE) at a time.
>
> > SGP_CACHE) < 0)
With SGP_CACHE, won't shmem_get_folio simply refuse to allocate
any pages beyond the end of the inode?
if (sgp <= SGP_CACHE &&
((loff_t)index << PAGE_SHIFT) >= i_size_read(inode))
return -EINVAL;
> > break;
> > if (filemap_check_wb_err(inode->i_mapping, 0)) {
> > @@ -267,7 +267,7 @@ xfile_get_folio(
> > i_size_write(inode, pos + len);
> >
> > pflags = memalloc_nofs_save();
> > - error = shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
> > + error = shmem_get_folio(inode, pos >> PAGE_SHIFT, 0,
> > &folio,
>
> This 0 could be pos + len, since the only caller is xfarray_sort,
> which
> runs much faster when it can heapsort a large folio's worth of data
> at a
> time.
>
> > (flags & XFILE_ALLOC) ? SGP_CACHE :
> > SGP_READ);
The same applies here.
> > memalloc_nofs_restore(pflags);
> > if (error)
> > diff --git a/fs/xfs/xfs_buf_mem.c b/fs/xfs/xfs_buf_mem.c
> > index 9bb2d24de709..07bebbfb16ee 100644
> > --- a/fs/xfs/xfs_buf_mem.c
> > +++ b/fs/xfs/xfs_buf_mem.c
> > @@ -149,7 +149,7 @@ xmbuf_map_page(
> > return -ENOMEM;
> > }
> >
> > - error = shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
> > SGP_CACHE);
> > + error = shmem_get_folio(inode, pos >> PAGE_SHIFT, 0,
> > &folio, SGP_CACHE);
>
> The "0" here could be (pos + BBTOB(bp->length)) since we're likely
> going
> to write there soon. Granted, no current user of xmbufs actually
> uses a
> blocksize larger than PAGE_SIZE, but in theory we could someday turn
> that on.
>
> Everything below here looks sane enough to me, but I'm not that much
> of
> an expert on mm/ things outside of the pagecache and shmem.c.
... and here.
XFS is no using an SGP flag that allows shmem_get_folio to allocate
a page beyond the end of the i_size.
--
All Rights Reversed.
