Patchwork [4/4] Btrfs: pass __GFP_WRITE for buffered write page allocations

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Submitter Johannes Weiner
Date Sept. 20, 2011, 1:45 p.m.
Message ID <1316526315-16801-5-git-send-email-jweiner@redhat.com>
Download mbox | patch
Permalink /patch/115535/
State Not Applicable
Headers show

Comments

Johannes Weiner - Sept. 20, 2011, 1:45 p.m.
Tell the page allocator that pages allocated for a buffered write are
expected to become dirty soon.

Signed-off-by: Johannes Weiner <jweiner@redhat.com>
---
 fs/btrfs/file.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
Johannes Weiner - Sept. 20, 2011, 1:56 p.m.
On Tue, Sep 20, 2011 at 03:45:15PM +0200, Johannes Weiner wrote:
> Tell the page allocator that pages allocated for a buffered write are
> expected to become dirty soon.
> 
> Signed-off-by: Johannes Weiner <jweiner@redhat.com>
> ---
>  fs/btrfs/file.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index e7872e4..ea1b892 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1084,7 +1084,7 @@ static noinline int prepare_pages(struct btrfs_root *root, struct file *file,
>  again:
>  	for (i = 0; i < num_pages; i++) {
>  		pages[i] = find_or_create_page(inode->i_mapping, index + i,
> -					       GFP_NOFS);
> +					       GFP_NOFS | __GFP_WRITE);

Btw and unrelated to this particular series, I think this should use
grab_cache_page_write_begin() in the first place.

Most grab_cache_page calls were replaced recently (a94733d "Btrfs: use
find_or_create_page instead of grab_cache_page") to be able to pass
GFP_NOFS, but the pages are now also no longer __GFP_HIGHMEM and
__GFP_MOVABLE, which irks both x86_32 and memory hotplug.

It might be better to change grab_cache_page instead to take a flags
argument that allows passing AOP_FLAG_NOFS and revert the sites back
to this helper?
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Josef Bacik - Sept. 20, 2011, 2:09 p.m.
On 09/20/2011 09:56 AM, Johannes Weiner wrote:
> On Tue, Sep 20, 2011 at 03:45:15PM +0200, Johannes Weiner wrote:
>> Tell the page allocator that pages allocated for a buffered write are
>> expected to become dirty soon.
>>
>> Signed-off-by: Johannes Weiner <jweiner@redhat.com>
>> ---
>>  fs/btrfs/file.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
>> index e7872e4..ea1b892 100644
>> --- a/fs/btrfs/file.c
>> +++ b/fs/btrfs/file.c
>> @@ -1084,7 +1084,7 @@ static noinline int prepare_pages(struct btrfs_root *root, struct file *file,
>>  again:
>>  	for (i = 0; i < num_pages; i++) {
>>  		pages[i] = find_or_create_page(inode->i_mapping, index + i,
>> -					       GFP_NOFS);
>> +					       GFP_NOFS | __GFP_WRITE);
> 
> Btw and unrelated to this particular series, I think this should use
> grab_cache_page_write_begin() in the first place.
> 
> Most grab_cache_page calls were replaced recently (a94733d "Btrfs: use
> find_or_create_page instead of grab_cache_page") to be able to pass
> GFP_NOFS, but the pages are now also no longer __GFP_HIGHMEM and
> __GFP_MOVABLE, which irks both x86_32 and memory hotplug.
> 
> It might be better to change grab_cache_page instead to take a flags
> argument that allows passing AOP_FLAG_NOFS and revert the sites back
> to this helper?

So I can do

pages[i] = grab_cache_page_write_begin(inode->i_mapping, index + i,
				       AOP_FLAG_NOFS);

right?  All we need is nofs, so I can just go through and change
everybody to that.  I'd rather not have to go through and change
grab_cache_page() to take a flags argument and change all the callers, I
have a bad habit of screwing stuff like that up :).  Thanks,

Josef
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Johannes Weiner - Sept. 20, 2011, 2:14 p.m.
On Tue, Sep 20, 2011 at 10:09:38AM -0400, Josef Bacik wrote:
> On 09/20/2011 09:56 AM, Johannes Weiner wrote:
> > On Tue, Sep 20, 2011 at 03:45:15PM +0200, Johannes Weiner wrote:
> >> Tell the page allocator that pages allocated for a buffered write are
> >> expected to become dirty soon.
> >>
> >> Signed-off-by: Johannes Weiner <jweiner@redhat.com>
> >> ---
> >>  fs/btrfs/file.c |    2 +-
> >>  1 files changed, 1 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> >> index e7872e4..ea1b892 100644
> >> --- a/fs/btrfs/file.c
> >> +++ b/fs/btrfs/file.c
> >> @@ -1084,7 +1084,7 @@ static noinline int prepare_pages(struct btrfs_root *root, struct file *file,
> >>  again:
> >>  	for (i = 0; i < num_pages; i++) {
> >>  		pages[i] = find_or_create_page(inode->i_mapping, index + i,
> >> -					       GFP_NOFS);
> >> +					       GFP_NOFS | __GFP_WRITE);
> > 
> > Btw and unrelated to this particular series, I think this should use
> > grab_cache_page_write_begin() in the first place.
> > 
> > Most grab_cache_page calls were replaced recently (a94733d "Btrfs: use
> > find_or_create_page instead of grab_cache_page") to be able to pass
> > GFP_NOFS, but the pages are now also no longer __GFP_HIGHMEM and
> > __GFP_MOVABLE, which irks both x86_32 and memory hotplug.
> > 
> > It might be better to change grab_cache_page instead to take a flags
> > argument that allows passing AOP_FLAG_NOFS and revert the sites back
> > to this helper?
> 
> So I can do
> 
> pages[i] = grab_cache_page_write_begin(inode->i_mapping, index + i,
> 				       AOP_FLAG_NOFS);
> 
> right?  All we need is nofs, so I can just go through and change
> everybody to that.

It does wait_on_page_writeback() in addition, so it may not be
appropriate for every callsite, I haven't checked.  But everything
that grabs a page for writing should be fine if you do it like this.

> I'd rather not have to go through and change grab_cache_page() to
> take a flags argument and change all the callers, I have a bad habit
> of screwing stuff like that up :).

Yeah, there are quite a few.  If we can get around it, all the better.

	Hannes
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Rik van Riel - Sept. 20, 2011, 6:41 p.m.
On 09/20/2011 09:45 AM, Johannes Weiner wrote:
> Tell the page allocator that pages allocated for a buffered write are
> expected to become dirty soon.
>
> Signed-off-by: Johannes Weiner<jweiner@redhat.com>

Reviewed-by: Rik van Riel <riel@redhat.com>
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Patch

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index e7872e4..ea1b892 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1084,7 +1084,7 @@  static noinline int prepare_pages(struct btrfs_root *root, struct file *file,
 again:
 	for (i = 0; i < num_pages; i++) {
 		pages[i] = find_or_create_page(inode->i_mapping, index + i,
-					       GFP_NOFS);
+					       GFP_NOFS | __GFP_WRITE);
 		if (!pages[i]) {
 			faili = i - 1;
 			err = -ENOMEM;