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Message-ID: <20240521163634.GT25518@frogsfrogsfrogs>
Date: Tue, 21 May 2024 09:36:34 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Daniel Gomez <da.gomez@...sung.com>
Cc: "hughd@...gle.com" <hughd@...gle.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"willy@...radead.org" <willy@...radead.org>,
"jack@...e.cz" <jack@...e.cz>,
"mcgrof@...nel.org" <mcgrof@...nel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
Pankaj Raghav <p.raghav@...sung.com>,
"dagmcr@...il.com" <dagmcr@...il.com>,
"yosryahmed@...gle.com" <yosryahmed@...gle.com>,
"baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>,
"ritesh.list@...il.com" <ritesh.list@...il.com>,
"lsf-pc@...ts.linux-foundation.org" <lsf-pc@...ts.linux-foundation.org>,
"david@...hat.com" <david@...hat.com>,
"chandan.babu@...cle.com" <chandan.babu@...cle.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"brauner@...nel.org" <brauner@...nel.org>
Subject: Re: [PATCH 11/12] shmem: add file length arg in shmem_get_folio()
path
On Tue, May 21, 2024 at 11:38:33AM +0000, Daniel Gomez wrote:
> On Fri, May 17, 2024 at 09:17:41AM -0700, Darrick J. Wong wrote:
> > On Wed, May 15, 2024 at 05:57:36AM +0000, Daniel Gomez wrote:
> > > In preparation for large folio in the write and fallocate paths, add
> > > file length argument in shmem_get_folio() path to be able to calculate
> > > the folio order based on the file size. Use of order-0 (PAGE_SIZE) for
> > > read, page cache read, and vm fault.
> > >
> > > This enables high order folios in the write and fallocate path once the
> > > folio order is calculated based on the length.
> > >
> > > Signed-off-by: Daniel Gomez <da.gomez@...sung.com>
> > > ---
> > > fs/xfs/scrub/xfile.c | 6 +++---
> > > fs/xfs/xfs_buf_mem.c | 3 ++-
> > > include/linux/shmem_fs.h | 2 +-
> > > mm/khugepaged.c | 3 ++-
> > > mm/shmem.c | 35 ++++++++++++++++++++---------------
> > > mm/userfaultfd.c | 2 +-
> > > 6 files changed, 29 insertions(+), 22 deletions(-)
> > >
> > > diff --git a/fs/xfs/scrub/xfile.c b/fs/xfs/scrub/xfile.c
> > > index 8cdd863db585..4905f5e4cb5d 100644
> > > --- a/fs/xfs/scrub/xfile.c
> > > +++ b/fs/xfs/scrub/xfile.c
> > > @@ -127,7 +127,7 @@ xfile_load(
> > > unsigned int offset;
> > >
> > > if (shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
> > > - SGP_READ) < 0)
> > > + SGP_READ, PAGE_SIZE) < 0)
> >
> > I suppose I /did/ say during LSFMM that for the current users of xfile.c
> > and xfs_buf_mem.c the order of the folio being returned doesn't really
> I not sure if I understood you well. Could you please elaborate on this?
Yes, I'll restate what I said in the session last week for those who
weren't there:
Currently, xfile.c and xfs_buf_mem.c are only used by online repair to
stage a recordset while rebuilding an ondisk btree index. IOWs, they're
ephemeral, so we don't care or need to optimize folio sizing. Some day
they might be adapted for longer-term usage though, so we might as well
try not to leave too many papercuts.
xfs_buf_mem.c creates in-memory btrees that mimic the ondisk btrees,
albeit with blocksize == PAGE_SIZE, regardless of the fs blocksize.
For this case we probably aren't ever going to care about large folios.
xfile.c is currently used to store fixed-size recordsets, names for
rebuilding directories, and name/value pairs for rebuilding xattr
structures. Records aren't allowed to be larger than PAGE_SIZE, names
cannot be larger than MAXNAMELEN (255), and xattr values can't be larger
than 64k.
For that last case maybe it might be nice to get a large folio to reduce
processing overhead, but huge xattrs aren't that common.
> > matter, but why wouldn't the last argument here be "roundup_64(count,
> > PAGE_SIZE)" ? Shouldn't we at least hint to the page cache about the
> > folio order that we actually want instead of limiting it to order-0?
>
> For v2, I'll include your suggestions. I think we can also enable large folios
> in xfile_get_folio(), please check below:
>
> diff --git a/fs/xfs/scrub/xfile.c b/fs/xfs/scrub/xfile.c
> index 8cdd863db585..df8b495b4939 100644
> --- a/fs/xfs/scrub/xfile.c
> +++ b/fs/xfs/scrub/xfile.c
> @@ -127,7 +127,7 @@ xfile_load(
> unsigned int offset;
>
> if (shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
> - SGP_READ) < 0)
> + SGP_READ, roundup_64(count, PAGE_SIZE)) < 0)
> break;
> if (!folio) {
> /*
> @@ -197,7 +197,7 @@ xfile_store(
> unsigned int offset;
>
> if (shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
> - SGP_CACHE) < 0)
> + SGP_CACHE, roundup_64(count, PAGE_SIZE)) < 0)
> break;
> if (filemap_check_wb_err(inode->i_mapping, 0)) {
> folio_unlock(folio);
> @@ -268,7 +268,8 @@ xfile_get_folio(
>
> pflags = memalloc_nofs_save();
> error = shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
> - (flags & XFILE_ALLOC) ? SGP_CACHE : SGP_READ);
> + (flags & XFILE_ALLOC) ? SGP_CACHE : SGP_READ,
> + roundup_64(i_size_read(inode), PAGE_SIZE));
I'm not sure why you picked i_size_read here; the xfile could be several
gigabytes long. xfile_get_folio want to look at a subset of the xfile,
not all of it.
roundup_64(len, PAGE_SIZE) perhaps?
Also, should the rounding be done inside the shmem code so that callers
don't have to know about that detail?
> memalloc_nofs_restore(pflags);
> if (error)
> return ERR_PTR(error);
>
> >
> > (Also it seems a little odd to me that the @index is in units of pgoff_t
> > but @len is in bytes.)
>
> I extended the shmem_get_folio() with @len to calculate folio order based on
> size (bytes). This is sent to ilog2() although I'm planning to use get_order()
> instead (after fixing the issues mentioned during the discussion). @index is
> used for __ffs() (same as in filemap).
>
> Would you use lofft for @len instead? Or what's your suggestion?
I was reacting to @index, not @len. I might've shifted @index to
"loff_t pos" but looking at the existing callsites it doesn't seem worth
the churn.
--D
> Thanks,
> Daniel
>
> >
> > > break;
> > > if (!folio) {
> > > /*
> > > @@ -197,7 +197,7 @@ xfile_store(
> > > unsigned int offset;
> > >
> > > if (shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
> > > - SGP_CACHE) < 0)
> > > + SGP_CACHE, PAGE_SIZE) < 0)
> > > break;
> > > if (filemap_check_wb_err(inode->i_mapping, 0)) {
> > > folio_unlock(folio);
> > > @@ -268,7 +268,7 @@ xfile_get_folio(
> > >
> > > pflags = memalloc_nofs_save();
> > > error = shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
> > > - (flags & XFILE_ALLOC) ? SGP_CACHE : SGP_READ);
> > > + (flags & XFILE_ALLOC) ? SGP_CACHE : SGP_READ, PAGE_SIZE);
> > > memalloc_nofs_restore(pflags);
> > > if (error)
> > > return ERR_PTR(error);
> > > diff --git a/fs/xfs/xfs_buf_mem.c b/fs/xfs/xfs_buf_mem.c
> > > index 9bb2d24de709..784c81d35a1f 100644
> > > --- a/fs/xfs/xfs_buf_mem.c
> > > +++ b/fs/xfs/xfs_buf_mem.c
> > > @@ -149,7 +149,8 @@ xmbuf_map_page(
> > > return -ENOMEM;
> > > }
> > >
> > > - error = shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio, SGP_CACHE);
> > > + error = shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio, SGP_CACHE,
> > > + PAGE_SIZE);
> >
> > This is ok unless someone wants to use a different XMBUF_BLOCKSIZE.
> >
> > --D
> >
> > > if (error)
> > > return error;
> > >
> > > diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> > > index 3fb18f7eb73e..bc59b4a00228 100644
> > > --- a/include/linux/shmem_fs.h
> > > +++ b/include/linux/shmem_fs.h
> > > @@ -142,7 +142,7 @@ enum sgp_type {
> > > };
> > >
> > > int shmem_get_folio(struct inode *inode, pgoff_t index, struct folio **foliop,
> > > - enum sgp_type sgp);
> > > + enum sgp_type sgp, size_t len);
> > > struct folio *shmem_read_folio_gfp(struct address_space *mapping,
> > > pgoff_t index, gfp_t gfp);
> > >
> > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > > index 38830174608f..947770ded68c 100644
> > > --- a/mm/khugepaged.c
> > > +++ b/mm/khugepaged.c
> > > @@ -1863,7 +1863,8 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
> > > xas_unlock_irq(&xas);
> > > /* swap in or instantiate fallocated page */
> > > if (shmem_get_folio(mapping->host, index,
> > > - &folio, SGP_NOALLOC)) {
> > > + &folio, SGP_NOALLOC,
> > > + PAGE_SIZE)) {
> > > result = SCAN_FAIL;
> > > goto xa_unlocked;
> > > }
> > > diff --git a/mm/shmem.c b/mm/shmem.c
> > > index d531018ffece..fcd2c9befe19 100644
> > > --- a/mm/shmem.c
> > > +++ b/mm/shmem.c
> > > @@ -1134,7 +1134,7 @@ static struct folio *shmem_get_partial_folio(struct inode *inode, pgoff_t index)
> > > * (although in some cases this is just a waste of time).
> > > */
> > > folio = NULL;
> > > - shmem_get_folio(inode, index, &folio, SGP_READ);
> > > + shmem_get_folio(inode, index, &folio, SGP_READ, PAGE_SIZE);
> > > return folio;
> > > }
> > >
> > > @@ -1844,7 +1844,7 @@ static struct folio *shmem_alloc_folio(gfp_t gfp, struct shmem_inode_info *info,
> > >
> > > static struct folio *shmem_alloc_and_add_folio(gfp_t gfp,
> > > struct inode *inode, pgoff_t index,
> > > - struct mm_struct *fault_mm, bool huge)
> > > + struct mm_struct *fault_mm, bool huge, size_t len)
> > > {
> > > struct address_space *mapping = inode->i_mapping;
> > > struct shmem_inode_info *info = SHMEM_I(inode);
> > > @@ -2173,7 +2173,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
> > > */
> > > static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
> > > struct folio **foliop, enum sgp_type sgp, gfp_t gfp,
> > > - struct vm_fault *vmf, vm_fault_t *fault_type)
> > > + struct vm_fault *vmf, vm_fault_t *fault_type, size_t len)
> > > {
> > > struct vm_area_struct *vma = vmf ? vmf->vma : NULL;
> > > struct mm_struct *fault_mm;
> > > @@ -2258,7 +2258,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
> > > huge_gfp = vma_thp_gfp_mask(vma);
> > > huge_gfp = limit_gfp_mask(huge_gfp, gfp);
> > > folio = shmem_alloc_and_add_folio(huge_gfp,
> > > - inode, index, fault_mm, true);
> > > + inode, index, fault_mm, true, len);
> > > if (!IS_ERR(folio)) {
> > > count_vm_event(THP_FILE_ALLOC);
> > > goto alloced;
> > > @@ -2267,7 +2267,8 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
> > > goto repeat;
> > > }
> > >
> > > - folio = shmem_alloc_and_add_folio(gfp, inode, index, fault_mm, false);
> > > + folio = shmem_alloc_and_add_folio(gfp, inode, index, fault_mm, false,
> > > + len);
> > > if (IS_ERR(folio)) {
> > > error = PTR_ERR(folio);
> > > if (error == -EEXIST)
> > > @@ -2377,10 +2378,10 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
> > > * Return: 0 if successful, else a negative error code.
> > > */
> > > int shmem_get_folio(struct inode *inode, pgoff_t index, struct folio **foliop,
> > > - enum sgp_type sgp)
> > > + enum sgp_type sgp, size_t len)
> > > {
> > > return shmem_get_folio_gfp(inode, index, foliop, sgp,
> > > - mapping_gfp_mask(inode->i_mapping), NULL, NULL);
> > > + mapping_gfp_mask(inode->i_mapping), NULL, NULL, len);
> > > }
> > > EXPORT_SYMBOL_GPL(shmem_get_folio);
> > >
> > > @@ -2475,7 +2476,7 @@ static vm_fault_t shmem_fault(struct vm_fault *vmf)
> > >
> > > WARN_ON_ONCE(vmf->page != NULL);
> > > err = shmem_get_folio_gfp(inode, vmf->pgoff, &folio, SGP_CACHE,
> > > - gfp, vmf, &ret);
> > > + gfp, vmf, &ret, PAGE_SIZE);
> > > if (err)
> > > return vmf_error(err);
> > > if (folio) {
> > > @@ -2954,6 +2955,9 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
> > > struct folio *folio;
> > > int ret = 0;
> > >
> > > + if (!mapping_large_folio_support(mapping))
> > > + len = min_t(size_t, len, PAGE_SIZE - offset_in_page(pos));
> > > +
> > > /* i_rwsem is held by caller */
> > > if (unlikely(info->seals & (F_SEAL_GROW |
> > > F_SEAL_WRITE | F_SEAL_FUTURE_WRITE))) {
> > > @@ -2963,7 +2967,7 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
> > > return -EPERM;
> > > }
> > >
> > > - ret = shmem_get_folio(inode, index, &folio, SGP_WRITE);
> > > + ret = shmem_get_folio(inode, index, &folio, SGP_WRITE, len);
> > > if (ret)
> > > return ret;
> > >
> > > @@ -3083,7 +3087,7 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> > > break;
> > > }
> > >
> > > - error = shmem_get_folio(inode, index, &folio, SGP_READ);
> > > + error = shmem_get_folio(inode, index, &folio, SGP_READ, PAGE_SIZE);
> > > if (error) {
> > > if (error == -EINVAL)
> > > error = 0;
> > > @@ -3260,7 +3264,7 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
> > > break;
> > >
> > > error = shmem_get_folio(inode, *ppos / PAGE_SIZE, &folio,
> > > - SGP_READ);
> > > + SGP_READ, PAGE_SIZE);
> > > if (error) {
> > > if (error == -EINVAL)
> > > error = 0;
> > > @@ -3469,7 +3473,8 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
> > > error = -ENOMEM;
> > > else
> > > error = shmem_get_folio(inode, index, &folio,
> > > - SGP_FALLOC);
> > > + SGP_FALLOC,
> > > + (end - index) << PAGE_SHIFT);
> > > if (error) {
> > > info->fallocend = undo_fallocend;
> > > /* Remove the !uptodate folios we added */
> > > @@ -3822,7 +3827,7 @@ static int shmem_symlink(struct mnt_idmap *idmap, struct inode *dir,
> > > } else {
> > > inode_nohighmem(inode);
> > > inode->i_mapping->a_ops = &shmem_aops;
> > > - error = shmem_get_folio(inode, 0, &folio, SGP_WRITE);
> > > + error = shmem_get_folio(inode, 0, &folio, SGP_WRITE, PAGE_SIZE);
> > > if (error)
> > > goto out_remove_offset;
> > > inode->i_op = &shmem_symlink_inode_operations;
> > > @@ -3868,7 +3873,7 @@ static const char *shmem_get_link(struct dentry *dentry, struct inode *inode,
> > > return ERR_PTR(-ECHILD);
> > > }
> > > } else {
> > > - error = shmem_get_folio(inode, 0, &folio, SGP_READ);
> > > + error = shmem_get_folio(inode, 0, &folio, SGP_READ, PAGE_SIZE);
> > > if (error)
> > > return ERR_PTR(error);
> > > if (!folio)
> > > @@ -5255,7 +5260,7 @@ struct folio *shmem_read_folio_gfp(struct address_space *mapping,
> > > int error;
> > >
> > > error = shmem_get_folio_gfp(inode, index, &folio, SGP_CACHE,
> > > - gfp, NULL, NULL);
> > > + gfp, NULL, NULL, PAGE_SIZE);
> > > if (error)
> > > return ERR_PTR(error);
> > >
> > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> > > index 3c3539c573e7..540a0c2d4325 100644
> > > --- a/mm/userfaultfd.c
> > > +++ b/mm/userfaultfd.c
> > > @@ -359,7 +359,7 @@ static int mfill_atomic_pte_continue(pmd_t *dst_pmd,
> > > struct page *page;
> > > int ret;
> > >
> > > - ret = shmem_get_folio(inode, pgoff, &folio, SGP_NOALLOC);
> > > + ret = shmem_get_folio(inode, pgoff, &folio, SGP_NOALLOC, PAGE_SIZE);
> > > /* Our caller expects us to return -EFAULT if we failed to find folio */
> > > if (ret == -ENOENT)
> > > ret = -EFAULT;
> > > --
> > > 2.43.0
> > >
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