[PATCH 0/3] Readahead fixes

[PATCH 0/3] Readahead fixes

[Raghavendra D Prabhu]

Minor readahead fixes, details in respective patch mails

Raghavendra D Prabhu (3):
  Change the check for PageReadahead into an else-if
  Remove file_ra_state from arguments of count_history_pages.
  Move the check for ra_pages after VM_SequentialReadHint()

 mm/filemap.c   |    8 ++++----
 mm/readahead.c |    3 +--
 2 files changed, 5 insertions(+), 6 deletions(-)

-- 
1.7.6

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[PATCH 1/3] mm/readahead: Change the check for PageReadahead into an else-if

[Raghavendra D Prabhu]

>From 51daa88ebd8e0d437289f589af29d4b39379ea76, page_sync_readahead coalesces
async readahead into its readahead window, so another checking for that again is
not required.

Signed-off-by: Raghavendra D Prabhu <rprabhu@wnohang.net>
---
 mm/filemap.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index a8251a8..074c23d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1115,8 +1115,7 @@ find_page:
 			page = find_get_page(mapping, index);
 			if (unlikely(page == NULL))
 				goto no_cached_page;
-		}
-		if (PageReadahead(page)) {
+		} else if (PageReadahead(page)) {
 			page_cache_async_readahead(mapping,
 					ra, filp, page,
 					index, last_index - index);
-- 
1.7.6

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Re: [PATCH 1/3] mm/readahead: Change the check for PageReadahead into an else-if

[Wu Fengguang]

On Sun, Jul 10, 2011 at 03:41:18AM +0800, Raghavendra D Prabhu wrote:
> >From 51daa88ebd8e0d437289f589af29d4b39379ea76, page_sync_readahead coalesces
> async readahead into its readahead window, so another checking for that again is
> not required.
> 
> Signed-off-by: Raghavendra D Prabhu <rprabhu@wnohang.net>

Acked-by: Wu Fengguang <fengguang.wu@intel.com>

Thank you!

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[PATCH 2/3] mm/readahead: Remove file_ra_state from arguments of count_history_pages.

[Raghavendra D Prabhu]

count_history_pages doesn't require readahead state to calculate the offset from history.

Signed-off-by: Raghavendra D Prabhu <rprabhu@wnohang.net>
---
 mm/readahead.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index 867f9dd..925d3b3 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -343,7 +343,6 @@ static unsigned long get_next_ra_size(struct file_ra_state *ra,
  * 	- thrashing threshold in memory tight systems
  */
 static pgoff_t count_history_pages(struct address_space *mapping,
-				   struct file_ra_state *ra,
 				   pgoff_t offset, unsigned long max)
 {
 	pgoff_t head;
@@ -366,7 +365,7 @@ static int try_context_readahead(struct address_space *mapping,
 {
 	pgoff_t size;
 
-	size = count_history_pages(mapping, ra, offset, max);
+	size = count_history_pages(mapping, offset, max);
 
 	/*
 	 * no history pages:
-- 
1.7.6

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Re: [PATCH 2/3] mm/readahead: Remove file_ra_state from arguments of count_history_pages.

[Wu Fengguang]

On Sun, Jul 10, 2011 at 03:41:19AM +0800, Raghavendra D Prabhu wrote:
> count_history_pages doesn't require readahead state to calculate the offset from history.
> 
> Signed-off-by: Raghavendra D Prabhu <rprabhu@wnohang.net>

Acked-by: Wu Fengguang <fengguang.wu@intel.com>

Thank you!

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[PATCH 3/3] mm/readahead: Move the check for ra_pages after VM_SequentialReadHint()

[Raghavendra D Prabhu]

page_cache_sync_readahead checks for ra->ra_pages again, so moving the check after VM_SequentialReadHint.

Signed-off-by: Raghavendra D Prabhu <rprabhu@wnohang.net>
---
 mm/filemap.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 074c23d..748f720 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1566,8 +1566,6 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
 	/* If we don't want any read-ahead, don't bother */
 	if (VM_RandomReadHint(vma))
 		return;
-	if (!ra->ra_pages)
-		return;
 
 	if (VM_SequentialReadHint(vma)) {
 		page_cache_sync_readahead(mapping, ra, file, offset,
@@ -1575,6 +1573,9 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
 		return;
 	}
 
+	if (!ra->ra_pages)
+		return;
+
 	/* Avoid banging the cache line if not needed */
 	if (ra->mmap_miss < MMAP_LOTSAMISS * 10)
 		ra->mmap_miss++;
-- 
1.7.6

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Re: [PATCH 3/3] mm/readahead: Move the check for ra_pages after VM_SequentialReadHint()

[Wu Fengguang]

On Sun, Jul 10, 2011 at 03:41:20AM +0800, Raghavendra D Prabhu wrote:
> page_cache_sync_readahead checks for ra->ra_pages again, so moving the check after VM_SequentialReadHint.

NAK. This patch adds nothing but overheads.

> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1566,8 +1566,6 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
>  	/* If we don't want any read-ahead, don't bother */
>  	if (VM_RandomReadHint(vma))
>  		return;
> -	if (!ra->ra_pages)
> -		return;
>  
>  	if (VM_SequentialReadHint(vma)) {
>  		page_cache_sync_readahead(mapping, ra, file, offset,
> @@ -1575,6 +1573,9 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
>  		return;
>  	}
>  
> +	if (!ra->ra_pages)
> +		return;
> +

page_cache_sync_readahead() has the same

	if (!ra->ra_pages)
		return;

So the patch adds the call into page_cache_sync_readahead() just to return..

Thanks,
Fengguang

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Re: [TOME] Re: [PATCH 3/3] mm/readahead: Move the check for ra_pages after VM_SequentialReadHint()

[Raghavendra D Prabhu]

[-- Attachment #1: Type: text/plain, Size: 1650 bytes --]

* On Sat, Jul 09, 2011 at 01:53:08PM -0700, Wu Fengguang <fengguang.wu@intel.com> wrote:
>On Sun, Jul 10, 2011 at 03:41:20AM +0800, Raghavendra D Prabhu wrote:
>> page_cache_sync_readahead checks for ra->ra_pages again, so moving the check after VM_SequentialReadHint.
>
>NAK. This patch adds nothing but overheads.
>
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -1566,8 +1566,6 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
>>  	/* If we don't want any read-ahead, don't bother */
>>  	if (VM_RandomReadHint(vma))
>>  		return;
>> -	if (!ra->ra_pages)
>> -		return;

>>  	if (VM_SequentialReadHint(vma)) {
>>  		page_cache_sync_readahead(mapping, ra, file, offset,
>> @@ -1575,6 +1573,9 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
>>  		return;
>>  	}

>> +	if (!ra->ra_pages)
>> +		return;
>> +
>
>page_cache_sync_readahead() has the same
>
>	if (!ra->ra_pages)
>		return;
1. Yes, I saw that and that is why I moved it after the condition, so that duplicate checks are
not needed -- ie., if VM_SequentialReadHint is true, then
(!ra->ra_pages) is checked twice otherwise.

2. Also, another thought, is the check needed at its original place (if
not it can be removed), reasons being -- filesystems like tmpfs which
have ra_pages set to 0 don't use filemap_fault in their VMA ops and also
do_sync_mmap_readahead is called in a major page fault context.
>
>So the patch adds the call into page_cache_sync_readahead() just to return..
>
>Thanks,
>Fengguang
>
--------------------------
Raghavendra Prabhu
GPG Id : 0xD72BE977
Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
www: wnohang.net

[-- Attachment #2: Type: application/pgp-signature, Size: 490 bytes --]

Re: [TOME] Re: [PATCH 3/3] mm/readahead: Move the check for ra_pages after VM_SequentialReadHint()

[Wu Fengguang]

On Sun, Jul 10, 2011 at 08:59:09PM +0800, Raghavendra D Prabhu wrote:
> * On Sat, Jul 09, 2011 at 01:53:08PM -0700, Wu Fengguang <fengguang.wu@intel.com> wrote:
> >On Sun, Jul 10, 2011 at 03:41:20AM +0800, Raghavendra D Prabhu wrote:
> >>page_cache_sync_readahead checks for ra->ra_pages again, so moving the check after VM_SequentialReadHint.
> >
> >NAK. This patch adds nothing but overheads.
> >
> >>--- a/mm/filemap.c
> >>+++ b/mm/filemap.c
> >>@@ -1566,8 +1566,6 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
> >> 	/* If we don't want any read-ahead, don't bother */
> >> 	if (VM_RandomReadHint(vma))
> >> 		return;
> >>-	if (!ra->ra_pages)
> >>-		return;
> 
> >> 	if (VM_SequentialReadHint(vma)) {
> >> 		page_cache_sync_readahead(mapping, ra, file, offset,
> >>@@ -1575,6 +1573,9 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
> >> 		return;
> >> 	}
> 
> >>+	if (!ra->ra_pages)
> >>+		return;
> >>+
> >
> >page_cache_sync_readahead() has the same
> >
> >	if (!ra->ra_pages)
> >		return;
> 1. Yes, I saw that and that is why I moved it after the condition, so that duplicate checks are
> not needed -- ie., if VM_SequentialReadHint is true, then
> (!ra->ra_pages) is checked twice otherwise.

Ok, I see.

> 2. Also, another thought, is the check needed at its original place (if
> not it can be removed), reasons being -- filesystems like tmpfs which
> have ra_pages set to 0 don't use filemap_fault in their VMA ops and also

Good point. tmpfs is using shmem_fault().. Can you remove the test?  

> do_sync_mmap_readahead is called in a major page fault context.

Right. This is irrelevant however, because if pa_pages==0, the
page faults will normally be major ones.

Thanks,
Fengguang

> >So the patch adds the call into page_cache_sync_readahead() just to return..
> >
> >Thanks,
> >Fengguang
> >
> --------------------------
> Raghavendra Prabhu
> GPG Id : 0xD72BE977
> Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
> www: wnohang.net


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Re. Revised [PATCH 3/3] mm/readahead: Remove the check for ra->ra_pages

[Raghavendra D Prabhu]

* On Sun, Jul 10, 2011 at 08:59:06AM -0700, Wu Fengguang <fengguang.wu@intel.com> wrote:
>On Sun, Jul 10, 2011 at 08:59:09PM +0800, Raghavendra D Prabhu wrote:
>> * On Sat, Jul 09, 2011 at 01:53:08PM -0700, Wu Fengguang <fengguang.wu@intel.com> wrote:
>> >On Sun, Jul 10, 2011 at 03:41:20AM +0800, Raghavendra D Prabhu wrote:
>> >>page_cache_sync_readahead checks for ra->ra_pages again, so moving the check after VM_SequentialReadHint.

>> >NAK. This patch adds nothing but overheads.

>> >>--- a/mm/filemap.c
>> >>+++ b/mm/filemap.c
>> >>@@ -1566,8 +1566,6 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
>> >> 	/* If we don't want any read-ahead, don't bother */
>> >> 	if (VM_RandomReadHint(vma))
>> >> 		return;
>> >>-	if (!ra->ra_pages)
>> >>-		return;

>> >> 	if (VM_SequentialReadHint(vma)) {
>> >> 		page_cache_sync_readahead(mapping, ra, file, offset,
>> >>@@ -1575,6 +1573,9 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
>> >> 		return;
>> >> 	}

>> >>+	if (!ra->ra_pages)
>> >>+		return;
>> >>+

>> >page_cache_sync_readahead() has the same

>> >	if (!ra->ra_pages)
>> >		return;
>> 1. Yes, I saw that and that is why I moved it after the condition, so that duplicate checks are
>> not needed -- ie., if VM_SequentialReadHint is true, then
>> (!ra->ra_pages) is checked twice otherwise.
>
>Ok, I see.
>
>> 2. Also, another thought, is the check needed at its original place (if
>> not it can be removed), reasons being -- filesystems like tmpfs which
>> have ra_pages set to 0 don't use filemap_fault in their VMA ops and also
>
>Good point. tmpfs is using shmem_fault().. Can you remove the test?
I have removed that test. Patch attached.
>
>> do_sync_mmap_readahead is called in a major page fault context.
>
>Right. This is irrelevant however, because if pa_pages==0, the
>page faults will normally be major ones.
>
>Thanks,
>Fengguang
>
>> >So the patch adds the call into page_cache_sync_readahead() just to return..

>> >Thanks,
>> >Fengguang

>> --------------------------
>> Raghavendra Prabhu
>> GPG Id : 0xD72BE977
>> Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
>> www: wnohang.net
>
>
======================================================================
  The check for ra->ra_pages is not required since fs like tmpfs which have
  ra_pages set to 0 don't use filemap_fault as part of their VMA ops (it uses
  shmem_fault). Also, page_cache_sync_readahead does its own check for ra_pages.

  Signed-off-by: Raghavendra D Prabhu <rprabhu@wnohang.net>
  ---
   mm/filemap.c |    2 --
   1 files changed, 0 insertions(+), 2 deletions(-)

  diff --git a/mm/filemap.c b/mm/filemap.c
  index 074c23d..0bcd276 100644
  --- a/mm/filemap.c
  +++ b/mm/filemap.c
  @@ -1566,8 +1566,6 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma,
          /* If we don't want any read-ahead, don't bother */
          if (VM_RandomReadHint(vma))
                  return;
  -       if (!ra->ra_pages)
  -               return;

          if (VM_SequentialReadHint(vma)) {
                  page_cache_sync_readahead(mapping, ra, file, offset,
  --
  1.7.6


--------------------------
Raghavendra Prabhu
GPG Id : 0xD72BE977
Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
www: wnohang.net

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Re: Re. Revised [PATCH 3/3] mm/readahead: Remove the check for ra->ra_pages

[Wu Fengguang]

>  The check for ra->ra_pages is not required since fs like tmpfs which have
>  ra_pages set to 0 don't use filemap_fault as part of their VMA ops (it uses
>  shmem_fault). Also, page_cache_sync_readahead does its own check for ra_pages.
> 
>  Signed-off-by: Raghavendra D Prabhu <rprabhu@wnohang.net>

Acked-by: Wu Fengguang <fengguang.wu@intel.com>

Thank you!

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