All of lore.kernel.org
 help / color / mirror / Atom feed
From: Joao Martins <joao.m.martins@oracle.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: linux-mm@kvack.org, linux-nvdimm@lists.01.org,
	Matthew Wilcox <willy@infradead.org>,
	Muchun Song <songmuchun@bytedance.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Daniel Jordan <daniel.m.jordan@oracle.com>,
	John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH RFC 7/9] mm/gup: Decrement head page once for group of subpages
Date: Thu, 17 Dec 2020 19:05:37 +0000	[thread overview]
Message-ID: <cf5585f0-1352-e3ab-9dbf-0185ad0a1b31@oracle.com> (raw)
In-Reply-To: <20201208193446.GP5487@ziepe.ca>

On 12/8/20 7:34 PM, Jason Gunthorpe wrote:
>> @@ -274,6 +291,7 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
>>  				 bool make_dirty)
>>  {
>>  	unsigned long index;
>> +	int refs = 1;
>>  
>>  	/*
>>  	 * TODO: this can be optimized for huge pages: if a series of pages is
>> @@ -286,8 +304,9 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
>>  		return;
>>  	}
>>  
>> -	for (index = 0; index < npages; index++) {
>> +	for (index = 0; index < npages; index += refs) {
>>  		struct page *page = compound_head(pages[index]);
>> +
> 
> I think this is really hard to read, it should end up as some:
> 
> for_each_compond_head(page_list, page_list_len, &head, &ntails) {
>        		if (!PageDirty(head))
> 			set_page_dirty_lock(head, ntails);
> 		unpin_user_page(head, ntails);
> }
> 
> And maybe you open code that iteration, but that basic idea to find a
> compound_head and ntails should be computational work performed.
> 
> No reason not to fix set_page_dirty_lock() too while you are here.
> 

The wack of atomics you mentioned earlier you referred to, I suppose it
ends being account_page_dirtied(). See partial diff at the end.

I was looking at the latter part and renaming all the fs that supply
set_page_dirty()... But now my concern is whether it's really safe to
assume that filesystems that supply it ... have indeed the ability to dirty
@ntails pages. Functionally, fixing set_page_dirty_lock() means we don't call
set_page_dirty(head) @ntails times as it happens today, we would only call once
with ntails as argument.

Perhaps the safest thing to do is still to iterate over
@ntails and call .set_page_dirty(page) and instead introduce
a set_page_range_dirty() which individual filesystems can separately
supply and give precedence of ->set_page_range_dirty() as opposed
to ->set_page_dirty() ?

	Joao

--------------------->8------------------------------

diff --git a/mm/gup.c b/mm/gup.c
index 41ab3d48e1bb..5f8a0f16ab62 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -295,7 +295,7 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long
npages,
                 * next writeback cycle. This is harmless.
                 */
                if (!PageDirty(head))
-                       set_page_dirty_lock(head);
+                       set_page_range_dirty_lock(head, ntails);
                put_compound_head(head, ntails, FOLL_PIN);
        }
 }
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 088729ea80b2..4642d037f657 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2417,7 +2417,8 @@ int __set_page_dirty_no_writeback(struct page *page, unsigned int
ntails)
  *
  * NOTE: This relies on being atomic wrt interrupts.
  */
-void account_page_dirtied(struct page *page, struct address_space *mapping)
+void account_page_dirtied(struct page *page, struct address_space *mapping,
+                         unsigned int ntails)
 {
        struct inode *inode = mapping->host;

@@ -2425,17 +2426,18 @@ void account_page_dirtied(struct page *page, struct address_space
*mapping)

        if (mapping_can_writeback(mapping)) {
                struct bdi_writeback *wb;
+               int nr = ntails + 1;

                inode_attach_wb(inode, page);
                wb = inode_to_wb(inode);

-               __inc_lruvec_page_state(page, NR_FILE_DIRTY);
-               __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
-               __inc_node_page_state(page, NR_DIRTIED);
-               inc_wb_stat(wb, WB_RECLAIMABLE);
-               inc_wb_stat(wb, WB_DIRTIED);
-               task_io_account_write(PAGE_SIZE);
-               current->nr_dirtied++;
+               mod_lruvec_page_state(page, NR_FILE_DIRTY, nr);
+               mod_zone_page_state(page_zone(page), NR_ZONE_WRITE_PENDING, nr);
+               mod_node_page_state(page_pgdat(page), NR_DIRTIED, nr);
+               __add_wb_stat(wb, WB_RECLAIMABLE, nr);
+               __add_wb_stat(wb, WB_DIRTIED, nr);
+               task_io_account_write(nr * PAGE_SIZE);
+               current->nr_dirtied += nr;
                this_cpu_inc(bdp_ratelimits);

                mem_cgroup_track_foreign_dirty(page, wb);
@@ -2485,7 +2487,7 @@ int __set_page_dirty_nobuffers(struct page *page, unsigned int ntails)
                xa_lock_irqsave(&mapping->i_pages, flags);
                BUG_ON(page_mapping(page) != mapping);
                WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
-               account_page_dirtied(page, mapping);
+               account_page_dirtied(page, mapping, ntails);
                __xa_set_mark(&mapping->i_pages, page_index(page),
                                   PAGECACHE_TAG_DIRTY);
                xa_unlock_irqrestore(&mapping->i_pages, flags);
@@ -2624,6 +2626,27 @@ int set_page_dirty_lock(struct page *page)
 }
 EXPORT_SYMBOL(set_page_dirty_lock);

+/*
+ * set_page_range_dirty() is racy if the caller has no reference against
+ * page->mapping->host, and if the page is unlocked.  This is because another
+ * CPU could truncate the page off the mapping and then free the mapping.
+ *
+ * Usually, the page _is_ locked, or the caller is a user-space process which
+ * holds a reference on the inode by having an open file.
+ *
+ * In other cases, the page should be locked before running set_page_range_dirty().
+ */
+int set_page_range_dirty_lock(struct page *page, unsigned int ntails)
+{
+       int ret;
+
+       lock_page(page);
+       ret = set_page_range_dirty(page, ntails);
+       unlock_page(page);
+       return ret;
+}
+EXPORT_SYMBOL(set_page_range_dirty_lock);
+
_______________________________________________
Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org
To unsubscribe send an email to linux-nvdimm-leave@lists.01.org

WARNING: multiple messages have this Message-ID
From: Joao Martins <joao.m.martins@oracle.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: linux-mm@kvack.org, Dan Williams <dan.j.williams@intel.com>,
	Ira Weiny <ira.weiny@intel.com>,
	linux-nvdimm@lists.01.org, Matthew Wilcox <willy@infradead.org>,
	Jane Chu <jane.chu@oracle.com>,
	Muchun Song <songmuchun@bytedance.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Daniel Jordan <daniel.m.jordan@oracle.com>,
	John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH RFC 7/9] mm/gup: Decrement head page once for group of subpages
Date: Thu, 17 Dec 2020 19:05:37 +0000	[thread overview]
Message-ID: <cf5585f0-1352-e3ab-9dbf-0185ad0a1b31@oracle.com> (raw)
In-Reply-To: <20201208193446.GP5487@ziepe.ca>

On 12/8/20 7:34 PM, Jason Gunthorpe wrote:
>> @@ -274,6 +291,7 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
>>  				 bool make_dirty)
>>  {
>>  	unsigned long index;
>> +	int refs = 1;
>>  
>>  	/*
>>  	 * TODO: this can be optimized for huge pages: if a series of pages is
>> @@ -286,8 +304,9 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
>>  		return;
>>  	}
>>  
>> -	for (index = 0; index < npages; index++) {
>> +	for (index = 0; index < npages; index += refs) {
>>  		struct page *page = compound_head(pages[index]);
>> +
> 
> I think this is really hard to read, it should end up as some:
> 
> for_each_compond_head(page_list, page_list_len, &head, &ntails) {
>        		if (!PageDirty(head))
> 			set_page_dirty_lock(head, ntails);
> 		unpin_user_page(head, ntails);
> }
> 
> And maybe you open code that iteration, but that basic idea to find a
> compound_head and ntails should be computational work performed.
> 
> No reason not to fix set_page_dirty_lock() too while you are here.
> 

The wack of atomics you mentioned earlier you referred to, I suppose it
ends being account_page_dirtied(). See partial diff at the end.

I was looking at the latter part and renaming all the fs that supply
set_page_dirty()... But now my concern is whether it's really safe to
assume that filesystems that supply it ... have indeed the ability to dirty
@ntails pages. Functionally, fixing set_page_dirty_lock() means we don't call
set_page_dirty(head) @ntails times as it happens today, we would only call once
with ntails as argument.

Perhaps the safest thing to do is still to iterate over
@ntails and call .set_page_dirty(page) and instead introduce
a set_page_range_dirty() which individual filesystems can separately
supply and give precedence of ->set_page_range_dirty() as opposed
to ->set_page_dirty() ?

	Joao

--------------------->8------------------------------

diff --git a/mm/gup.c b/mm/gup.c
index 41ab3d48e1bb..5f8a0f16ab62 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -295,7 +295,7 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long
npages,
                 * next writeback cycle. This is harmless.
                 */
                if (!PageDirty(head))
-                       set_page_dirty_lock(head);
+                       set_page_range_dirty_lock(head, ntails);
                put_compound_head(head, ntails, FOLL_PIN);
        }
 }
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 088729ea80b2..4642d037f657 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2417,7 +2417,8 @@ int __set_page_dirty_no_writeback(struct page *page, unsigned int
ntails)
  *
  * NOTE: This relies on being atomic wrt interrupts.
  */
-void account_page_dirtied(struct page *page, struct address_space *mapping)
+void account_page_dirtied(struct page *page, struct address_space *mapping,
+                         unsigned int ntails)
 {
        struct inode *inode = mapping->host;

@@ -2425,17 +2426,18 @@ void account_page_dirtied(struct page *page, struct address_space
*mapping)

        if (mapping_can_writeback(mapping)) {
                struct bdi_writeback *wb;
+               int nr = ntails + 1;

                inode_attach_wb(inode, page);
                wb = inode_to_wb(inode);

-               __inc_lruvec_page_state(page, NR_FILE_DIRTY);
-               __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
-               __inc_node_page_state(page, NR_DIRTIED);
-               inc_wb_stat(wb, WB_RECLAIMABLE);
-               inc_wb_stat(wb, WB_DIRTIED);
-               task_io_account_write(PAGE_SIZE);
-               current->nr_dirtied++;
+               mod_lruvec_page_state(page, NR_FILE_DIRTY, nr);
+               mod_zone_page_state(page_zone(page), NR_ZONE_WRITE_PENDING, nr);
+               mod_node_page_state(page_pgdat(page), NR_DIRTIED, nr);
+               __add_wb_stat(wb, WB_RECLAIMABLE, nr);
+               __add_wb_stat(wb, WB_DIRTIED, nr);
+               task_io_account_write(nr * PAGE_SIZE);
+               current->nr_dirtied += nr;
                this_cpu_inc(bdp_ratelimits);

                mem_cgroup_track_foreign_dirty(page, wb);
@@ -2485,7 +2487,7 @@ int __set_page_dirty_nobuffers(struct page *page, unsigned int ntails)
                xa_lock_irqsave(&mapping->i_pages, flags);
                BUG_ON(page_mapping(page) != mapping);
                WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
-               account_page_dirtied(page, mapping);
+               account_page_dirtied(page, mapping, ntails);
                __xa_set_mark(&mapping->i_pages, page_index(page),
                                   PAGECACHE_TAG_DIRTY);
                xa_unlock_irqrestore(&mapping->i_pages, flags);
@@ -2624,6 +2626,27 @@ int set_page_dirty_lock(struct page *page)
 }
 EXPORT_SYMBOL(set_page_dirty_lock);

+/*
+ * set_page_range_dirty() is racy if the caller has no reference against
+ * page->mapping->host, and if the page is unlocked.  This is because another
+ * CPU could truncate the page off the mapping and then free the mapping.
+ *
+ * Usually, the page _is_ locked, or the caller is a user-space process which
+ * holds a reference on the inode by having an open file.
+ *
+ * In other cases, the page should be locked before running set_page_range_dirty().
+ */
+int set_page_range_dirty_lock(struct page *page, unsigned int ntails)
+{
+       int ret;
+
+       lock_page(page);
+       ret = set_page_range_dirty(page, ntails);
+       unlock_page(page);
+       return ret;
+}
+EXPORT_SYMBOL(set_page_range_dirty_lock);
+


  parent reply	other threads:[~2020-12-17 19:08 UTC|newest]

Thread overview: 147+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-08 17:28 [PATCH RFC 0/9] mm, sparse-vmemmap: Introduce compound pagemaps Joao Martins
2020-12-08 17:28 ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 1/9] memremap: add ZONE_DEVICE support for compound pages Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-09  5:59   ` John Hubbard
2020-12-09  5:59     ` John Hubbard
2020-12-09  6:33     ` Matthew Wilcox
2020-12-09  6:33       ` Matthew Wilcox
2020-12-09 13:12       ` Joao Martins
2020-12-09 13:12         ` Joao Martins
2021-02-20  1:43     ` Dan Williams
2021-02-20  1:43       ` Dan Williams
2021-02-22 11:24       ` Joao Martins
2021-02-22 11:24         ` Joao Martins
2021-02-22 20:37         ` Dan Williams
2021-02-22 20:37           ` Dan Williams
2021-02-23 15:46           ` Joao Martins
2021-02-23 15:46             ` Joao Martins
2021-02-23 16:50             ` Dan Williams
2021-02-23 16:50               ` Dan Williams
2021-02-23 17:18               ` Joao Martins
2021-02-23 17:18                 ` Joao Martins
2021-02-23 18:18                 ` Dan Williams
2021-02-23 18:18                   ` Dan Williams
2021-03-10 18:12           ` Joao Martins
2021-03-10 18:12             ` Joao Martins
2021-03-12  5:54             ` Dan Williams
2021-03-12  5:54               ` Dan Williams
2021-02-20  1:24   ` Dan Williams
2021-02-20  1:24     ` Dan Williams
2021-02-22 11:09     ` Joao Martins
2021-02-22 11:09       ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 2/9] sparse-vmemmap: Consolidate arguments in vmemmap section populate Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-09  6:16   ` John Hubbard
2020-12-09  6:16     ` John Hubbard
2020-12-09 13:51     ` Joao Martins
2020-12-09 13:51       ` Joao Martins
2021-02-20  1:49   ` Dan Williams
2021-02-20  1:49     ` Dan Williams
2021-02-22 11:26     ` Joao Martins
2021-02-22 11:26       ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 3/9] sparse-vmemmap: Reuse vmemmap areas for a given mhp_params::align Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-08 17:38   ` Joao Martins
2020-12-08 17:38     ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 3/9] sparse-vmemmap: Reuse vmemmap areas for a given page size Joao Martins
2020-12-08 17:28   ` Joao Martins
2021-02-20  3:34   ` Dan Williams
2021-02-20  3:34     ` Dan Williams
2021-02-22 11:42     ` Joao Martins
2021-02-22 11:42       ` Joao Martins
2021-02-22 22:40       ` Dan Williams
2021-02-22 22:40         ` Dan Williams
2021-02-23 15:46         ` Joao Martins
2021-02-23 15:46           ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 4/9] mm/page_alloc: Reuse tail struct pages for compound pagemaps Joao Martins
2020-12-08 17:28   ` Joao Martins
2021-02-20  6:17   ` Dan Williams
2021-02-20  6:17     ` Dan Williams
2021-02-22 12:01     ` Joao Martins
2021-02-22 12:01       ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 5/9] device-dax: Compound pagemap support Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 6/9] mm/gup: Grab head page refcount once for group of subpages Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-08 19:49   ` Jason Gunthorpe
2020-12-09 11:05     ` Joao Martins
2020-12-09 11:05       ` Joao Martins
2020-12-09 15:15       ` Jason Gunthorpe
2020-12-09 16:02         ` Joao Martins
2020-12-09 16:02           ` Joao Martins
2020-12-09 16:24           ` Jason Gunthorpe
2020-12-09 17:27             ` Joao Martins
2020-12-09 17:27               ` Joao Martins
2020-12-09 18:14             ` Matthew Wilcox
2020-12-09 18:14               ` Matthew Wilcox
2020-12-09 19:08               ` Jason Gunthorpe
2020-12-10 15:43               ` Joao Martins
2020-12-10 15:43                 ` Joao Martins
2020-12-09  4:40   ` John Hubbard
2020-12-09  4:40     ` John Hubbard
2020-12-09 13:44     ` Joao Martins
2020-12-09 13:44       ` Joao Martins
2020-12-08 17:28 ` [PATCH RFC 7/9] mm/gup: Decrement head page " Joao Martins
2020-12-08 17:28   ` Joao Martins
2020-12-08 19:34   ` Jason Gunthorpe
2020-12-09  5:06     ` John Hubbard
2020-12-09  5:06       ` John Hubbard
2020-12-09 13:43       ` Jason Gunthorpe
2020-12-09 12:17     ` Joao Martins
2020-12-09 12:17       ` Joao Martins
2020-12-17 19:05     ` Joao Martins [this message]
2020-12-17 19:05       ` Joao Martins
2020-12-17 20:05       ` Jason Gunthorpe
2020-12-17 22:34         ` Joao Martins
2020-12-17 22:34           ` Joao Martins
2020-12-18 14:25           ` Jason Gunthorpe
2020-12-19  2:06         ` John Hubbard
2020-12-19  2:06           ` John Hubbard
2020-12-19 13:10           ` Joao Martins
2020-12-19 13:10             ` Joao Martins
2020-12-08 17:29 ` [PATCH RFC 8/9] RDMA/umem: batch page unpin in __ib_mem_release() Joao Martins
2020-12-08 17:29   ` Joao Martins
2020-12-08 19:29   ` Jason Gunthorpe
2020-12-09 10:59     ` Joao Martins
2020-12-09 10:59       ` Joao Martins
2020-12-19 13:15       ` Joao Martins
2020-12-19 13:15         ` Joao Martins
2020-12-09  5:18   ` John Hubbard
2020-12-09  5:18     ` John Hubbard
2020-12-08 17:29 ` [PATCH RFC 9/9] mm: Add follow_devmap_page() for devdax vmas Joao Martins
2020-12-08 17:29   ` Joao Martins
2020-12-08 19:57   ` Jason Gunthorpe
2020-12-09  8:05     ` Christoph Hellwig
2020-12-09  8:05       ` Christoph Hellwig
2020-12-09 11:19     ` Joao Martins
2020-12-09 11:19       ` Joao Martins
2020-12-09  5:23   ` John Hubbard
2020-12-09  5:23     ` John Hubbard
2020-12-09  9:38 ` [PATCH RFC 0/9] mm, sparse-vmemmap: Introduce compound pagemaps David Hildenbrand
2020-12-09  9:38   ` David Hildenbrand
2020-12-09  9:52 ` [External] " Muchun Song
2020-12-09  9:52   ` Muchun Song
2021-02-20  1:18 ` Dan Williams
2021-02-20  1:18   ` Dan Williams
2021-02-22 11:06   ` Joao Martins
2021-02-22 11:06     ` Joao Martins
2021-02-22 14:32     ` Joao Martins
2021-02-22 14:32       ` Joao Martins
2021-02-23 16:28   ` Joao Martins
2021-02-23 16:28     ` Joao Martins
2021-02-23 16:44     ` Dan Williams
2021-02-23 16:44       ` Dan Williams
2021-02-23 17:15       ` Joao Martins
2021-02-23 17:15         ` Joao Martins
2021-02-23 18:15         ` Dan Williams
2021-02-23 18:15           ` Dan Williams
2021-02-23 18:54       ` Jason Gunthorpe
2021-02-23 22:48         ` Dan Williams
2021-02-23 22:48           ` Dan Williams
2021-02-23 23:07           ` Jason Gunthorpe
2021-02-24  0:14             ` Dan Williams
2021-02-24  0:14               ` Dan Williams
2021-02-24  1:00               ` Jason Gunthorpe
2021-02-24  1:32                 ` Dan Williams
2021-02-24  1:32                   ` Dan Williams

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=cf5585f0-1352-e3ab-9dbf-0185ad0a1b31@oracle.com \
    --to=joao.m.martins@oracle.com \
    --cc=akpm@linux-foundation.org \
    --cc=daniel.m.jordan@oracle.com \
    --cc=jgg@ziepe.ca \
    --cc=jhubbard@nvidia.com \
    --cc=linux-mm@kvack.org \
    --cc=linux-nvdimm@lists.01.org \
    --cc=mike.kravetz@oracle.com \
    --cc=songmuchun@bytedance.com \
    --cc=willy@infradead.org \
    --subject='Re: [PATCH RFC 7/9] mm/gup: Decrement head page once for group of subpages' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.