Re: [PATCH v8 01/10] fs: Allow fine-grained control of folio sizes

Pankaj Raghav (Samsung)
2024-07-09T21:08:43Z

> >
> > - We make THP an explicit dependency for XFS:
> >
> > diff --git a/fs/xfs/Kconfig b/fs/xfs/Kconfig
> > index d41edd30388b7..be2c1c0e9fe8b 100644
> > --- a/fs/xfs/Kconfig
> > +++ b/fs/xfs/Kconfig
> > @@ -5,6 +5,7 @@ config XFS_FS
> > select EXPORTFS
> > select LIBCRC32C
> > select FS_IOMAP
> > + select TRANSPARENT_HUGEPAGE
> > help
> > XFS is a high performance journaling filesystem which originated
> > on the SGI IRIX platform. It is completely multi-threaded, can
> >
> > OR
> >
> > We create a helper in page cache that FSs can use to check if a specific
> > order can be supported at mount time:
>
> I like this solution better; if XFS is going to drop support for o[ld]d
> architectures I think we need /some/ sort of notice period. Or at least
> a better story than "we want to support 64k fsblocks on x64 so we're
> withdrawing support even for 4k fsblocks and smallish filesystems on
> m68k".
>
> You probably don't want bs>ps support to block on some arcane discussion
> about 32-bit, right? ;)
>

:)

> > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> > index 14e1415f7dcf..9be775ef11a5 100644
> > --- a/include/linux/pagemap.h
> > +++ b/include/linux/pagemap.h
> > @@ -374,6 +374,14 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
> > #define MAX_XAS_ORDER (XA_CHUNK_SHIFT * 2 - 1)
> > #define MAX_PAGECACHE_ORDER min(MAX_XAS_ORDER, PREFERRED_MAX_PAGECACHE_ORDER)
> >
> > +
> > +static inline unsigned int mapping_max_folio_order_supported()
> > +{
> > + if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
> > + return 0;
>
> Shouldn't this line be indented by two tabs, not six spaces?
>
> > + return MAX_PAGECACHE_ORDER;
> > +}
>
> Alternately, should this return the max folio size in bytes?
>
> static inline size_t mapping_max_folio_size(void)
> {
> if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
> return 1U << (PAGE_SHIFT + MAX_PAGECACHE_ORDER);
> return PAGE_SIZE;
> }

We already have mapping_max_folio_size(mapping) which returns the
maximum folio order set for that mapping. So this could be called as
mapping_max_folio_size_supported().

So we could just have mapping_max_folio_size_supported() instead of
having mapping_max_folio_order_supported as you suggest.

>
> Then the validation looks like:
>
> const size_t max_folio_size = mapping_max_folio_size();
>
> if (mp->m_sb.sb_blocksize > max_folio_size) {
> xfs_warn(mp,
> "block size (%u bytes) not supported; maximum folio size is %u.",
> mp->m_sb.sb_blocksize, max_folio_size);
> error = -ENOSYS;
> goto out_free_sb;
> }
>
> (Don't mind me bikeshedding here.)
>
> > +
> >
> >
> > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> > index b8a93a8f35cac..e2be8743c2c20 100644
> > --- a/fs/xfs/xfs_super.c
> > +++ b/fs/xfs/xfs_super.c
> > @@ -1647,6 +1647,15 @@ xfs_fs_fill_super(
> > goto out_free_sb;
> > }
> >
> > + if (mp->m_sb.sb_blocklog - PAGE_SHIFT >
> > + mapping_max_folio_order_supported()) {
> > + xfs_warn(mp,
> > +"Block Size (%d bytes) is not supported. Check MAX_PAGECACHE_ORDER",
> > + mp->m_sb.sb_blocksize);
>
> You might as well print MAX_PAGECACHE_ORDER here to make analysis
> easier on less-familiar architectures:

Yes!

>
> xfs_warn(mp,
> "block size (%d bytes) is not supported; max folio size is %u.",
> mp->m_sb.sb_blocksize,
> 1U << mapping_max_folio_order_supported());
>
> (I wrote this comment first.)

>
> --D
>
> > + error = -ENOSYS;
> > + goto out_free_sb;
> > + }
> > +
> > xfs_warn(mp,
> > "EXPERIMENTAL: V5 Filesystem with Large Block Size (%d bytes) enabled.",
> > mp->m_sb.sb_blocksize);
> >
> >
> > --
> > Pankaj