From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 09/15] mm: Allow large pages to be added to the page cache
Date: Thu, 26 Sep 2019 17:22:58 +0300 [thread overview]
Message-ID: <20190926142258.tzjqedcbptr4tvg4@box> (raw)
In-Reply-To: <20190925005214.27240-10-willy@infradead.org>
On Tue, Sep 24, 2019 at 05:52:08PM -0700, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
>
> We return -EEXIST if there are any non-shadow entries in the page
> cache in the range covered by the large page. If there are multiple
> shadow entries in the range, we set *shadowp to one of them (currently
> the one at the highest index). If that turns out to be the wrong
> answer, we can implement something more complex. This is mostly
> modelled after the equivalent function in the shmem code.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> mm/filemap.c | 37 ++++++++++++++++++++++++++-----------
> 1 file changed, 26 insertions(+), 11 deletions(-)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index bab97addbb1d..afe8f5d95810 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -855,6 +855,7 @@ static int __add_to_page_cache_locked(struct page *page,
> int huge = PageHuge(page);
> struct mem_cgroup *memcg;
> int error;
> + unsigned int nr = 1;
> void *old;
>
> VM_BUG_ON_PAGE(!PageLocked(page), page);
> @@ -866,31 +867,45 @@ static int __add_to_page_cache_locked(struct page *page,
> gfp_mask, &memcg, false);
> if (error)
> return error;
> + xas_set_order(&xas, offset, compound_order(page));
> + nr = compound_nr(page);
> }
>
> - get_page(page);
> + page_ref_add(page, nr);
> page->mapping = mapping;
> page->index = offset;
>
> do {
> + unsigned long exceptional = 0;
> + unsigned int i = 0;
> +
> xas_lock_irq(&xas);
> - old = xas_load(&xas);
> - if (old && !xa_is_value(old))
> + xas_for_each_conflict(&xas, old) {
> + if (!xa_is_value(old))
> + break;
> + exceptional++;
> + if (shadowp)
> + *shadowp = old;
> + }
> + if (old)
> xas_set_err(&xas, -EEXIST);
This made me confused.
Do we rely on 'old' to be NULL if the loop has completed without 'break'?
It's not very obvious.
Can we have a comment or call xas_set_err() within the loop next to the
'break'?
> - xas_store(&xas, page);
> + xas_create_range(&xas);
> if (xas_error(&xas))
> goto unlock;
>
> - if (xa_is_value(old)) {
> - mapping->nrexceptional--;
> - if (shadowp)
> - *shadowp = old;
> +next:
> + xas_store(&xas, page);
> + if (++i < nr) {
> + xas_next(&xas);
> + goto next;
> }
> - mapping->nrpages++;
> + mapping->nrexceptional -= exceptional;
> + mapping->nrpages += nr;
>
> /* hugetlb pages do not participate in page cache accounting */
> if (!huge)
> - __inc_node_page_state(page, NR_FILE_PAGES);
> + __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES,
> + nr);
We also need to bump NR_FILE_THPS here.
> unlock:
> xas_unlock_irq(&xas);
> } while (xas_nomem(&xas, gfp_mask & GFP_RECLAIM_MASK));
> @@ -907,7 +922,7 @@ static int __add_to_page_cache_locked(struct page *page,
> /* Leave page->index set: truncation relies upon it */
> if (!huge)
> mem_cgroup_cancel_charge(page, memcg, false);
> - put_page(page);
> + page_ref_sub(page, nr);
> return xas_error(&xas);
> }
> ALLOW_ERROR_INJECTION(__add_to_page_cache_locked, ERRNO);
> --
> 2.23.0
>
>
--
Kirill A. Shutemov
next prev parent reply other threads:[~2019-09-26 14:22 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-25 0:51 [RFC 00/15] Large pages in the page-cache Matthew Wilcox
2019-09-25 0:52 ` [PATCH 01/15] mm: Use vm_fault error code directly Matthew Wilcox
2019-09-26 13:55 ` Kirill A. Shutemov
2019-09-25 0:52 ` [PATCH 02/15] fs: Introduce i_blocks_per_page Matthew Wilcox
2019-09-25 8:36 ` Dave Chinner
2019-10-04 19:28 ` Matthew Wilcox
2019-10-08 3:53 ` Dave Chinner
2019-09-25 0:52 ` [PATCH 03/15] mm: Add file_offset_of_ helpers Matthew Wilcox
2019-09-26 14:02 ` Kirill A. Shutemov
2019-10-04 19:39 ` Matthew Wilcox
2019-09-25 0:52 ` [PATCH 04/15] iomap: Support large pages Matthew Wilcox
2019-09-25 0:52 ` [PATCH 05/15] xfs: " Matthew Wilcox
2019-09-25 0:52 ` [PATCH 06/15] xfs: Pass a page to xfs_finish_page_writeback Matthew Wilcox
2019-09-25 0:52 ` [PATCH 07/15] mm: Make prep_transhuge_page tail-callable Matthew Wilcox
2019-09-26 14:13 ` Kirill A. Shutemov
2019-09-25 0:52 ` [PATCH 08/15] mm: Add __page_cache_alloc_order Matthew Wilcox
2019-09-26 14:15 ` Kirill A. Shutemov
2019-09-25 0:52 ` [PATCH 09/15] mm: Allow large pages to be added to the page cache Matthew Wilcox
2019-09-26 14:22 ` Kirill A. Shutemov [this message]
2019-09-25 0:52 ` [PATCH 10/15] mm: Allow find_get_page to be used for large pages Matthew Wilcox
2019-10-01 10:32 ` Kirill A. Shutemov
2019-09-25 0:52 ` [PATCH 11/15] mm: Remove hpage_nr_pages Matthew Wilcox
2019-10-01 10:35 ` Kirill A. Shutemov
2019-09-25 0:52 ` [PATCH 12/15] mm: Support removing arbitrary sized pages from mapping Matthew Wilcox
2019-10-01 10:39 ` Kirill A. Shutemov
2019-09-25 0:52 ` [PATCH 13/15] mm: Add a huge page fault handler for files Matthew Wilcox
2019-10-01 10:42 ` Kirill A. Shutemov
2019-09-25 0:52 ` [PATCH 14/15] mm: Align THP mappings for non-DAX Matthew Wilcox
2019-10-01 10:45 ` Kirill A. Shutemov
2019-10-01 11:21 ` William Kucharski
2019-10-01 11:32 ` Kirill A. Shutemov
2019-10-01 12:18 ` William Kucharski
2019-10-01 14:20 ` Kirill A. Shutemov
2019-10-01 16:08 ` William Kucharski
2019-10-02 0:15 ` Kirill A. Shutemov
2019-09-25 0:52 ` [PATCH 15/15] xfs: Use filemap_huge_fault Matthew Wilcox
2019-10-02 13:07 ` [PATCH 03/15] mm: Add file_offset_of_ helpers Hillf Danton
2019-10-04 19:33 ` Matthew Wilcox
2019-10-02 13:32 ` [PATCH 04/15] iomap: Support large pages Hillf Danton
2019-10-04 19:34 ` Matthew Wilcox
2019-10-03 4:08 ` [PATCH 06/15] xfs: Pass a page to xfs_finish_page_writeback Hillf Danton
2019-10-04 19:35 ` Matthew Wilcox
2019-10-03 5:08 ` [PATCH 11/15] mm: Remove hpage_nr_pages Hillf Danton
2019-10-04 19:36 ` Matthew Wilcox
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