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Message-ID: <487c0bec-4229-4add-bec4-1711f0b9bbee@suse.de>
Date: Tue, 13 Feb 2024 13:20:50 +0100
From: Hannes Reinecke <hare@...e.de>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc: mcgrof@...nel.org, gost.dev@...sung.com, akpm@...ux-foundation.org,
kbusch@...nel.org, djwong@...nel.org, chandan.babu@...cle.com,
p.raghav@...sung.com, linux-kernel@...r.kernel.org, willy@...radead.org,
linux-mm@...ck.org, david@...morbit.com
Subject: Re: [RFC v2 02/14] filemap: align the index to mapping_min_order in
the page cache
On 2/13/24 10:37, Pankaj Raghav (Samsung) wrote:
> From: Luis Chamberlain <mcgrof@...nel.org>
>
> Supporting mapping_min_order implies that we guarantee each folio in the
> page cache has at least an order of mapping_min_order. So when adding new
> folios to the page cache we must ensure the index used is aligned to the
> mapping_min_order as the page cache requires the index to be aligned to
> the order of the folio.
>
> A higher order folio than min_order by definition is a multiple of the
> min_order. If an index is aligned to an order higher than a min_order, it
> will also be aligned to the min order.
>
> This effectively introduces no new functional changes when min order is
> not set other than a few rounding computations that should result in the
> same value.
>
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
> ---
> mm/filemap.c | 34 ++++++++++++++++++++++++++--------
> 1 file changed, 26 insertions(+), 8 deletions(-)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 750e779c23db..323a8e169581 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2479,14 +2479,16 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
> {
> struct file *filp = iocb->ki_filp;
> struct address_space *mapping = filp->f_mapping;
> + unsigned int min_nrpages = mapping_min_folio_nrpages(mapping);
> struct file_ra_state *ra = &filp->f_ra;
> - pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
> + pgoff_t index = round_down(iocb->ki_pos >> PAGE_SHIFT, min_nrpages);
> pgoff_t last_index;
> struct folio *folio;
> int err = 0;
>
> /* "last_index" is the index of the page beyond the end of the read */
> last_index = DIV_ROUND_UP(iocb->ki_pos + count, PAGE_SIZE);
> + last_index = round_up(last_index, min_nrpages);
Huh? 'last_index' is unset here; sure you mean 'iocb->ki_pos + count' ?
And what's the rationale to replace 'DIV_ROUND_UP' with 'round_up' ?
> retry:
> if (fatal_signal_pending(current))
> return -EINTR;
> @@ -2502,8 +2504,7 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
> if (!folio_batch_count(fbatch)) {
> if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
> return -EAGAIN;
> - err = filemap_create_folio(filp, mapping,
> - iocb->ki_pos >> PAGE_SHIFT, fbatch);
> + err = filemap_create_folio(filp, mapping, index, fbatch);
> if (err == AOP_TRUNCATED_PAGE)
> goto retry;
> return err;
> @@ -3095,7 +3096,10 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
> struct file *file = vmf->vma->vm_file;
> struct file_ra_state *ra = &file->f_ra;
> struct address_space *mapping = file->f_mapping;
> - DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff);
> + unsigned int min_order = mapping_min_folio_order(mapping);
> + unsigned int min_nrpages = mapping_min_folio_nrpages(file->f_mapping);
> + pgoff_t index = round_down(vmf->pgoff, min_nrpages);
> + DEFINE_READAHEAD(ractl, file, ra, mapping, index);
> struct file *fpin = NULL;
> unsigned long vm_flags = vmf->vma->vm_flags;
> unsigned int mmap_miss;
> @@ -3147,10 +3151,11 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
> */
> fpin = maybe_unlock_mmap_for_io(vmf, fpin);
> ra->start = max_t(long, 0, vmf->pgoff - ra->ra_pages / 2);
> + ra->start = round_down(ra->start, min_nrpages);
> ra->size = ra->ra_pages;
> ra->async_size = ra->ra_pages / 4;
> ractl._index = ra->start;
> - page_cache_ra_order(&ractl, ra, 0);
> + page_cache_ra_order(&ractl, ra, min_order);
> return fpin;
> }
>
> @@ -3164,7 +3169,9 @@ static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
> {
> struct file *file = vmf->vma->vm_file;
> struct file_ra_state *ra = &file->f_ra;
> - DEFINE_READAHEAD(ractl, file, ra, file->f_mapping, vmf->pgoff);
> + unsigned int min_nrpages = mapping_min_folio_nrpages(file->f_mapping);
> + pgoff_t index = round_down(vmf->pgoff, min_nrpages);
> + DEFINE_READAHEAD(ractl, file, ra, file->f_mapping, index);
> struct file *fpin = NULL;
> unsigned int mmap_miss;
>
> @@ -3212,13 +3219,17 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
> struct file *file = vmf->vma->vm_file;
> struct file *fpin = NULL;
> struct address_space *mapping = file->f_mapping;
> + unsigned int min_order = mapping_min_folio_order(mapping);
> + unsigned int nrpages = 1UL << min_order;
> struct inode *inode = mapping->host;
> - pgoff_t max_idx, index = vmf->pgoff;
> + pgoff_t max_idx, index = round_down(vmf->pgoff, nrpages);
> struct folio *folio;
> vm_fault_t ret = 0;
> bool mapping_locked = false;
>
> max_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
> + max_idx = round_up(max_idx, nrpages);
> +
Same here.
(And the additional whitespace can probably go ...)
> if (unlikely(index >= max_idx))
> return VM_FAULT_SIGBUS;
>
> @@ -3317,13 +3328,17 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
> * We must recheck i_size under page lock.
> */
> max_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
> + max_idx = round_up(max_idx, nrpages);
> +
See above.
> if (unlikely(index >= max_idx)) {
> folio_unlock(folio);
> folio_put(folio);
> return VM_FAULT_SIGBUS;
> }
>
> - vmf->page = folio_file_page(folio, index);
> + VM_BUG_ON_FOLIO(folio_order(folio) < min_order, folio);
> +
> + vmf->page = folio_file_page(folio, vmf->pgoff);
> return ret | VM_FAULT_LOCKED;
>
> page_not_uptodate:
> @@ -3658,6 +3673,9 @@ static struct folio *do_read_cache_folio(struct address_space *mapping,
> {
> struct folio *folio;
> int err;
> + unsigned int min_nrpages = mapping_min_folio_nrpages(mapping);
> +
> + index = round_down(index, min_nrpages);
>
> if (!filler)
> filler = mapping->a_ops->read_folio;
Cheers,
Hannes
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