[PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[Peng Tao]

Asking for layout in pg_init will always make client ask for only 4KB
layout in every layoutget. This way, client drops the IO size information
that is meaningful for MDS in handing out layout.

In stead, if layout is not find in cache, do not send layoutget
at once. Wait until before issuing IO in pnfs_do_multiple_reads/writes
because that is where we know the real size of current IO. By telling the
real IO size to MDS, MDS will have a better chance to give proper layout.

Signed-off-by: Peng Tao <peng_tao@emc.com>
---
Resend to fix patch title. Sorry for the noise...

 fs/nfs/blocklayout/blocklayout.c |   54 ++++++++++++++++++++++++++++++++++++-
 1 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/blocklayout/blocklayout.c b/fs/nfs/blocklayout/blocklayout.c
index 48cfac3..fd585fe 100644
--- a/fs/nfs/blocklayout/blocklayout.c
+++ b/fs/nfs/blocklayout/blocklayout.c
@@ -39,6 +39,7 @@
 #include <linux/prefetch.h>
 
 #include "blocklayout.h"
+#include "../internal.h"
 
 #define NFSDBG_FACILITY	NFSDBG_PNFS_LD
 
@@ -990,14 +991,63 @@ bl_clear_layoutdriver(struct nfs_server *server)
 	return 0;
 }
 
+/* While RFC doesn't limit maximum size of layout, we better limit it ourself. */
+#define PNFSBLK_MAXRSIZE (0x1<<22)
+#define PNFSBLK_MAXWSIZE (0x1<<21)
+static void
+bl_pg_init_read(struct nfs_pageio_descriptor *pgio, struct nfs_page *req)
+{
+	struct inode *ino = pgio->pg_inode;
+	struct pnfs_layout_hdr *lo;
+
+	BUG_ON(pgio->pg_lseg != NULL);
+	spin_lock(&ino->i_lock);
+	lo = pnfs_find_alloc_layout(ino, req->wb_context, GFP_KERNEL);
+	if (!lo || test_bit(lo_fail_bit(IOMODE_READ), &lo->plh_flags)) {
+		spin_unlock(&ino->i_lock);
+		nfs_pageio_reset_read_mds(pgio);
+		return;
+	}
+
+	pgio->pg_bsize = PNFSBLK_MAXRSIZE;
+	pgio->pg_lseg = pnfs_find_get_layout_locked(ino,
+						req_offset(req),
+						req->wb_bytes,
+						IOMODE_READ);
+	spin_unlock(&ino->i_lock);
+}
+
+static void
+bl_pg_init_write(struct nfs_pageio_descriptor *pgio, struct nfs_page *req)
+{
+	struct inode *ino = pgio->pg_inode;
+	struct pnfs_layout_hdr *lo;
+
+	BUG_ON(pgio->pg_lseg != NULL);
+	spin_lock(&ino->i_lock);
+	lo = pnfs_find_alloc_layout(ino, req->wb_context, GFP_NOFS);
+	if (!lo || test_bit(lo_fail_bit(IOMODE_RW), &lo->plh_flags)) {
+		spin_unlock(&ino->i_lock);
+		nfs_pageio_reset_write_mds(pgio);
+		return;
+	}
+
+	pgio->pg_bsize = PNFSBLK_MAXWSIZE;
+	pgio->pg_lseg = pnfs_find_get_layout_locked(ino,
+						req_offset(req),
+						req->wb_bytes,
+						IOMODE_RW);
+	spin_unlock(&ino->i_lock);
+}
+
 static const struct nfs_pageio_ops bl_pg_read_ops = {
-	.pg_init = pnfs_generic_pg_init_read,
+	.pg_init = bl_pg_init_read,
 	.pg_test = pnfs_generic_pg_test,
 	.pg_doio = pnfs_generic_pg_readpages,
 };
 
 static const struct nfs_pageio_ops bl_pg_write_ops = {
-	.pg_init = pnfs_generic_pg_init_write,
+	.pg_init = bl_pg_init_write,
 	.pg_test = pnfs_generic_pg_test,
 	.pg_doio = pnfs_generic_pg_writepages,
 };
-- 
1.7.1.262.g5ef3d

Re: [PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[Jim Rees]

Peng Tao wrote:

  Asking for layout in pg_init will always make client ask for only 4KB
  layout in every layoutget. This way, client drops the IO size information
  that is meaningful for MDS in handing out layout.
  
  In stead, if layout is not find in cache, do not send layoutget
  at once. Wait until before issuing IO in pnfs_do_multiple_reads/writes
  because that is where we know the real size of current IO. By telling the
  real IO size to MDS, MDS will have a better chance to give proper layout.
  
  Signed-off-by: Peng Tao <peng_tao@emc.com>
  ---
  Resend to fix patch title. Sorry for the noise...

You may want to fix the patch date too, on this series and the other series
you sent earlier (later?).  I know China is in a later timezone but I don't
think it's that much later.

RE: [PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[tao.peng]

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Re: [PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[Benny Halevy]

On 2011-12-03 06:56, Peng Tao wrote:
> Asking for layout in pg_init will always make client ask for only 4KB
> layout in every layoutget. This way, client drops the IO size information
> that is meaningful for MDS in handing out layout.
> 
> In stead, if layout is not find in cache, do not send layoutget
> at once. Wait until before issuing IO in pnfs_do_multiple_reads/writes
> because that is where we know the real size of current IO. By telling the
> real IO size to MDS, MDS will have a better chance to give proper layout.
> 
> Signed-off-by: Peng Tao <peng_tao@emc.com>
> ---
> Resend to fix patch title. Sorry for the noise...
> 
>  fs/nfs/blocklayout/blocklayout.c |   54 ++++++++++++++++++++++++++++++++++++-
>  1 files changed, 52 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfs/blocklayout/blocklayout.c b/fs/nfs/blocklayout/blocklayout.c
> index 48cfac3..fd585fe 100644
> --- a/fs/nfs/blocklayout/blocklayout.c
> +++ b/fs/nfs/blocklayout/blocklayout.c
> @@ -39,6 +39,7 @@
>  #include <linux/prefetch.h>
>  
>  #include "blocklayout.h"
> +#include "../internal.h"
>  
>  #define NFSDBG_FACILITY	NFSDBG_PNFS_LD
>  
> @@ -990,14 +991,63 @@ bl_clear_layoutdriver(struct nfs_server *server)
>  	return 0;
>  }
>  
> +/* While RFC doesn't limit maximum size of layout, we better limit it ourself. */

Why is that?
What do these arbitrary numbers represent?
If these limits depend on some other system sizes they should reflect the dependency
as part of their calculation.

Benny

> +#define PNFSBLK_MAXRSIZE (0x1<<22)
> +#define PNFSBLK_MAXWSIZE (0x1<<21)
> +static void
> +bl_pg_init_read(struct nfs_pageio_descriptor *pgio, struct nfs_page *req)
> +{
> +	struct inode *ino = pgio->pg_inode;
> +	struct pnfs_layout_hdr *lo;
> +
> +	BUG_ON(pgio->pg_lseg != NULL);
> +	spin_lock(&ino->i_lock);
> +	lo = pnfs_find_alloc_layout(ino, req->wb_context, GFP_KERNEL);
> +	if (!lo || test_bit(lo_fail_bit(IOMODE_READ), &lo->plh_flags)) {
> +		spin_unlock(&ino->i_lock);
> +		nfs_pageio_reset_read_mds(pgio);
> +		return;
> +	}
> +
> +	pgio->pg_bsize = PNFSBLK_MAXRSIZE;
> +	pgio->pg_lseg = pnfs_find_get_layout_locked(ino,
> +						req_offset(req),
> +						req->wb_bytes,
> +						IOMODE_READ);
> +	spin_unlock(&ino->i_lock);
> +}
> +
> +static void
> +bl_pg_init_write(struct nfs_pageio_descriptor *pgio, struct nfs_page *req)
> +{
> +	struct inode *ino = pgio->pg_inode;
> +	struct pnfs_layout_hdr *lo;
> +
> +	BUG_ON(pgio->pg_lseg != NULL);
> +	spin_lock(&ino->i_lock);
> +	lo = pnfs_find_alloc_layout(ino, req->wb_context, GFP_NOFS);
> +	if (!lo || test_bit(lo_fail_bit(IOMODE_RW), &lo->plh_flags)) {
> +		spin_unlock(&ino->i_lock);
> +		nfs_pageio_reset_write_mds(pgio);
> +		return;
> +	}
> +
> +	pgio->pg_bsize = PNFSBLK_MAXWSIZE;
> +	pgio->pg_lseg = pnfs_find_get_layout_locked(ino,
> +						req_offset(req),
> +						req->wb_bytes,
> +						IOMODE_RW);
> +	spin_unlock(&ino->i_lock);
> +}
> +
>  static const struct nfs_pageio_ops bl_pg_read_ops = {
> -	.pg_init = pnfs_generic_pg_init_read,
> +	.pg_init = bl_pg_init_read,
>  	.pg_test = pnfs_generic_pg_test,
>  	.pg_doio = pnfs_generic_pg_readpages,
>  };
>  
>  static const struct nfs_pageio_ops bl_pg_write_ops = {
> -	.pg_init = pnfs_generic_pg_init_write,
> +	.pg_init = bl_pg_init_write,
>  	.pg_test = pnfs_generic_pg_test,
>  	.pg_doio = pnfs_generic_pg_writepages,
>  };

Re: [PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[Peng Tao]

On Wed, Nov 30, 2011 at 8:57 PM, Benny Halevy <bhalevy@tonian.com> wrote:
> On 2011-12-03 06:56, Peng Tao wrote:
>> Asking for layout in pg_init will always make client ask for only 4KB
>> layout in every layoutget. This way, client drops the IO size information
>> that is meaningful for MDS in handing out layout.
>>
>> In stead, if layout is not find in cache, do not send layoutget
>> at once. Wait until before issuing IO in pnfs_do_multiple_reads/writes
>> because that is where we know the real size of current IO. By telling the
>> real IO size to MDS, MDS will have a better chance to give proper layout.
>>
>> Signed-off-by: Peng Tao <peng_tao@emc.com>
>> ---
>> Resend to fix patch title. Sorry for the noise...
>>
>>  fs/nfs/blocklayout/blocklayout.c |   54 ++++++++++++++++++++++++++++++++++++-
>>  1 files changed, 52 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/nfs/blocklayout/blocklayout.c b/fs/nfs/blocklayout/blocklayout.c
>> index 48cfac3..fd585fe 100644
>> --- a/fs/nfs/blocklayout/blocklayout.c
>> +++ b/fs/nfs/blocklayout/blocklayout.c
>> @@ -39,6 +39,7 @@
>>  #include <linux/prefetch.h>
>>
>>  #include "blocklayout.h"
>> +#include "../internal.h"
>>
>>  #define NFSDBG_FACILITY      NFSDBG_PNFS_LD
>>
>> @@ -990,14 +991,63 @@ bl_clear_layoutdriver(struct nfs_server *server)
>>       return 0;
>>  }
>>
>> +/* While RFC doesn't limit maximum size of layout, we better limit it ourself. */
>
> Why is that?
> What do these arbitrary numbers represent?
> If these limits depend on some other system sizes they should reflect the dependency
> as part of their calculation.
What I wanted to add here is a limit to stop pg_test() (like object's
max_io_size) and 2MB is just an experience value...

Thanks,
Tao
>
> Benny
>
>> +#define PNFSBLK_MAXRSIZE (0x1<<22)
>> +#define PNFSBLK_MAXWSIZE (0x1<<21)
>> +static void
>> +bl_pg_init_read(struct nfs_pageio_descriptor *pgio, struct nfs_page *req)
>> +{
>> +     struct inode *ino = pgio->pg_inode;
>> +     struct pnfs_layout_hdr *lo;
>> +
>> +     BUG_ON(pgio->pg_lseg != NULL);
>> +     spin_lock(&ino->i_lock);
>> +     lo = pnfs_find_alloc_layout(ino, req->wb_context, GFP_KERNEL);
>> +     if (!lo || test_bit(lo_fail_bit(IOMODE_READ), &lo->plh_flags)) {
>> +             spin_unlock(&ino->i_lock);
>> +             nfs_pageio_reset_read_mds(pgio);
>> +             return;
>> +     }
>> +
>> +     pgio->pg_bsize = PNFSBLK_MAXRSIZE;
>> +     pgio->pg_lseg = pnfs_find_get_layout_locked(ino,
>> +                                             req_offset(req),
>> +                                             req->wb_bytes,
>> +                                             IOMODE_READ);
>> +     spin_unlock(&ino->i_lock);
>> +}
>> +
>> +static void
>> +bl_pg_init_write(struct nfs_pageio_descriptor *pgio, struct nfs_page *req)
>> +{
>> +     struct inode *ino = pgio->pg_inode;
>> +     struct pnfs_layout_hdr *lo;
>> +
>> +     BUG_ON(pgio->pg_lseg != NULL);
>> +     spin_lock(&ino->i_lock);
>> +     lo = pnfs_find_alloc_layout(ino, req->wb_context, GFP_NOFS);
>> +     if (!lo || test_bit(lo_fail_bit(IOMODE_RW), &lo->plh_flags)) {
>> +             spin_unlock(&ino->i_lock);
>> +             nfs_pageio_reset_write_mds(pgio);
>> +             return;
>> +     }
>> +
>> +     pgio->pg_bsize = PNFSBLK_MAXWSIZE;
>> +     pgio->pg_lseg = pnfs_find_get_layout_locked(ino,
>> +                                             req_offset(req),
>> +                                             req->wb_bytes,
>> +                                             IOMODE_RW);
>> +     spin_unlock(&ino->i_lock);
>> +}
>> +
>>  static const struct nfs_pageio_ops bl_pg_read_ops = {
>> -     .pg_init = pnfs_generic_pg_init_read,
>> +     .pg_init = bl_pg_init_read,
>>       .pg_test = pnfs_generic_pg_test,
>>       .pg_doio = pnfs_generic_pg_readpages,
>>  };
>>
>>  static const struct nfs_pageio_ops bl_pg_write_ops = {
>> -     .pg_init = pnfs_generic_pg_init_write,
>> +     .pg_init = bl_pg_init_write,
>>       .pg_test = pnfs_generic_pg_test,
>>       .pg_doio = pnfs_generic_pg_writepages,
>>  };



-- 
Thanks,
Tao

Re: [PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[Boaz Harrosh]

On 11/30/2011 05:17 AM, Peng Tao wrote:
>>>
>>> +/* While RFC doesn't limit maximum size of layout, we better limit it ourself. */
>>
>> Why is that?
>> What do these arbitrary numbers represent?
>> If these limits depend on some other system sizes they should reflect the dependency
>> as part of their calculation.
> What I wanted to add here is a limit to stop pg_test() (like object's
> max_io_size) and 2MB is just an experience value...
> 
> Thanks,
> Tao
>>
>> Benny
>>
>>> +#define PNFSBLK_MAXRSIZE (0x1<<22)
>>> +#define PNFSBLK_MAXWSIZE (0x1<<21)

You see this is the basic principal flaw of your scheme. It is equating IO sizes
with lseg sizes.

Lets back up for a second

A. First thing to understand is that any segmenting server be it blocks objects
   or files, will want the client to report to the best of it's knowledge
   the intention of the writing application. Therefor a solution should be
   good for all Three. What ever you are trying to do should not be private to
   blocks and must not conflict with other LO needs.

   Note: that the NFS-write-out stack since it holds back on writing until
   sync time or memory pressure that in most cases at the point of IO has at
   it's disposal the complete application IO in it's page collection per file.
   (Exception is very large writes which is fine to split, given resources condition
    on the client)

   So below when I say application we can later mean the complete page list
   available per inode at the time of write-out.

B. The *optimum* for any segmented server is:
   (and addressing Trond's concern of seg list exploding and never freeing up)

B.1. If an application will write O..N of the file
1. Get one lo_seg of 0..N
2. IO at max_io from O to N until done.
3. Return or forget the lo_seg

B.2. In the case of random IO O1..N1, O2..N2,..., On..Nn

For objects and files (segmented) the optimum is still:
1. Get one lo_seg of 01..Nn
2. IO at max_io for each Ox..Nx until done.
   (objects: max_io is a factor of BIO sizes group boundary and alignments.
    files: max_io is stripe_unit)
3. Return or forget the 1 lo_seg

For blocks the optimum is
1. Get n lo_segs of O1..N1, O2..N2,..., On..Nn
2. IO at max_io for each Ox..Nx until done.
3. Return or forget any Ox..Nx who's IO is done

You can see that stage 2. for any kind of LO and in either B.1 or B.2 cases
is the same. 
And this is, as the author intended, the .bg_init -> pg_test -> pg_IO.

For blocks with in .write_paglist there is an internal loop that re-slices the
requested linear pagelist to extents, possibly slicing each extent at bio_size
boundaries. At files and objects this slicing (though I admit very different)
actually happen at .pg_test, so at .write_paglist the request is sent in full.

C. So back to our problem:

C.1 NACK on your patchset. You are shouting to the roof how the client must
    report to the Server (as hint) to the best of it's knowledge what the
    application is going to do. And then you sneakily introduce an IO_MAX limitation.

    This you MUST fix. Ether you send good server hint for the anticipated
    application IO or not at all.

    (The Server can always introduce it's own slicing and limits)

    You did all this because you have circumvented the chance to do so at .pg_test
    because you want the .bg_init -> pg_test -> pg_IO. loop to be your 
    O1..N1, O2..N2,...,On..Nn parser.

C.2 You must work out a system which will satisfy not only blocks (MPFS) server
    But any segmenting server out there. blocks objects or files (segmented)
    By reporting the best information you have and letting the Server do it's
    decisions.

    Now by postponing the report to after .pg_test -> .pg_IO you break the way
    objects and files IO slicing works, and leaves them in the dark. I'm not sure
    you really mean that each LO needs to do it's own private hacks?


C.3 Say we go back to the drawing board and want to do the stage 1 above of
    sending the exact information to server, be it B.1 or B.2.

    a. We want it at .pg_init so we have a layout at .pg_test to inspect.

       Done properly will let you, in blocks, slice by extents at .pg_test
       and .write_pages can send the complete paglist to md (bio chaining)

    b. Say theoretically that we are willing to spend CPU and memory to collect
       that information, like for example also pre-loop the page-list and/or
       call the LO for the final decision.

    So my all point is that b. above should eventually happen but efficiently by
    pre-collecting some counters. (Remember that we already saw all these pages
    in generic nfs at the vfs .write_pages vector)

    Then since .pg_init is already called into LO, just change the API so the
    LO have all the needed information available be it B.1 or B.2 and in return
    will pass on to pnfs.c the actual lo_seg size optimal. In B.1 they all
    send the same thing. In B.2 they differ.

    We can start by doing all the API changes so .pg_init can specify and
    return the suggested lo_size. And perhaps we add to the nfs_pageio_descriptor,
    passed to .pg_init, a couple of members describing above
    O1 - the index of the first page
    N1 - The length up to the firs hole
    Nn - Highest written page

    
    At first version:
      A good approximation which gives you an exact middle point
      between blocks B.2 and objects/files B.2, is dirty count.
    At later patch:
      Have generic NFS collect the above O1, N1, and Nn for you and base
      your decision on that.


And stop the private blocks hacks and the IO_MAX capping on the lo_seg
size.

Boaz

RE: [PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[tao.peng]

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Re: [PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[Benny Halevy]

On 2011-12-01 07:05, tao.peng@emc.com wrote:
> 1. remove the limit on IO_MAX at .pg_test.
> 2. ask for layout at .pg_doio for the size of current IO desc
> 3. if server returns short layout, split nfs_read/write_data or desc and issue the pagelist covered by lseg.
> 4. do 2 and 3 in a loop until all pages in current desc is handled.

Sounds reasonable to me.

Benny

Re: [PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[Boaz Harrosh]

On 11/30/2011 09:05 PM, tao.peng@emc.com wrote:
>> -----Original Message-----
> Why return or forget the 1 lo_seg? What you really need to avoid seg
> list exploding is to have LRU based caching and merge them when
> necessary, instead of asking and dropping lseg again and again...
> 

Ya Ya, I'm talking in abstract now giving the all picture. If in our
above case the application has closed the file and will not ever open it
again then I'm right, right? of course once you got it you can keep it
around in a cache. Though I think that with heavy segmenting keeping segs
passed ROC is extremely harder to manage. Be careful with that in current
implementation.

> Removing the IO_MAX limitation can be a second optimization. I was
> hoping to remove it if current IO_MAX thing turns out hurting
> performance. And one reason for IO_MAX is to avoid the likelihood
> that server returns short layout, because current implementation is
> limited to retry nfs_read/write_data as a whole instead of splitting
> it up. I think that if we do it this way, the IO_MAX can be removed
> later when necessary, by introducing a splitting mechanism either on
> nfs_read/write_data or on desc. Now that you ask for it, I think
> following approach is possible:
>
> 1. remove the limit on IO_MAX at .pg_test.
> 2. ask for layout at .pg_doio for the size of current IO desc
> 3. if server returns short layout, split nfs_read/write_data or desc and issue the pagelist covered by lseg.
> 4. do 2 and 3 in a loop until all pages in current desc is handled.
> 

So in effect you are doing what I suggest two passes 
one: what's the next hole,
second: Collect pages slicing by returned lo_seg

Don't you think it is more simple to do a 3 line preliminary
loop in "one:"?

and keep the current code that is now exactly built to do
"second:"

You are suggesting to effectively repeat current code using
the first .pg_init...pg_doio for one: and hacking for blocks
"second:"

I want 3 lines of code for one: and keep second: exactly as is.

<snip>

> Looks like you are suggesting going through the dirty page list twice
> before issuing IO, one just for getting the IO size information and
> another one for page collapsing. The whole point of moving layoutget
> to .pg_doio is to collect real IO size there because we don't know it
> at .pg_init. And it is done without any changes to generic NFS IO
> path. I'm not sure if it is appropriate to change generic IO routine
> to collect the information before .pg_init (I'd be happy too if we
> can do it there).

That's what you are suggesting as well look in your step 4.:
	do 2 and 3 in a loop until all pages in current desc is handled
sounds like another loop on all pages no?

BTW: we are already doing two passes in the system we already looked
through all the pages when building the io desc at .write/read_pages

At first we can do above 3 lines loop in .pg_init. Second we can
just collect that information in generic nfs at the first loop
we are already doing

>>
>>     a. We want it at .pg_init so we have a layout at .pg_test to inspect.
>>
>>        Done properly will let you, in blocks, slice by extents at .pg_test
>>        and .write_pages can send the complete paglist to md (bio chaining)
>>
> Unlike objects and files, blocks don't slice by extents, not at .pg_test, nor at .read/write_pagelist.
>  

What? What do you do? Send a scsi scatter list command?
I don't think so. Somewhere you have to see an extent boundary of the data
and send the continue of the next extent on disk as a new block request
in a new bio with a new disk offset. No?

I'm not saying to do this right away, but you could simplify the code a lot
by slicing by extent inside .pg_test

<>
>>
>>     At first version:
>>       A good approximation which gives you an exact middle point
>>       between blocks B.2 and objects/files B.2, is dirty count.
>>     At later patch:
>>       Have generic NFS collect the above O1, N1, and Nn for you and base
>>       your decision on that.
>>
>
> Well, unless you put both the two parts in... The first version is
> ignoring the fact that blocks MDS cannot give out file stripping
> information as easily as objects and files do. And I will stand
> against it alone because all it does is to benefit objects while
> hurting blocks (files don't care because they use whole file layout,
> at least for now).

Lets make a computerize lets find O1..N1 and put in the Generic
code for everyone objects files-segmented and blocks. Because I
need it two. And I'd like O1..Nn but for first step I'd love
O1..N1 a lot.

Please see my point. You created a system that only blocks can
benefit from unless objects repeats the same exact but duplicated
hacks as blocks.

Please do the *very* simple thing I suggest which we can all enjoy.

> 
> Otherwise, I would suggest having private hack for blocks because we have a real problem to solve.
> 

It's just as real for objects, and files when they will do segments.

My suggestion is to have two helpers at pnfs.c one for blocks and
objects, one for files. Which can be called in .pg_init.
The blocks/objects does a simple loop counting the first contiguous
chunk and asks for a layout, like today. files one just sends
all-file request.

Boaz

Re: [PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[Boaz Harrosh]

On 12/01/2011 09:33 AM, Boaz Harrosh wrote:
> On 11/30/2011 09:05 PM, tao.peng@emc.com wrote:
>>> -----Original Message-----
>> Why return or forget the 1 lo_seg? What you really need to avoid seg
>> list exploding is to have LRU based caching and merge them when
>> necessary, instead of asking and dropping lseg again and again...
>>
> 
> Ya Ya, I'm talking in abstract now giving the all picture. If in our
> above case the application has closed the file and will not ever open it
> again then I'm right, right? of course once you got it you can keep it
> around in a cache. Though I think that with heavy segmenting keeping segs
> passed ROC is extremely harder to manage. Be careful with that in current
> implementation.
> 
>> Removing the IO_MAX limitation can be a second optimization. I was
>> hoping to remove it if current IO_MAX thing turns out hurting
>> performance. And one reason for IO_MAX is to avoid the likelihood
>> that server returns short layout, because current implementation is
>> limited to retry nfs_read/write_data as a whole instead of splitting
>> it up. I think that if we do it this way, the IO_MAX can be removed
>> later when necessary, by introducing a splitting mechanism either on
>> nfs_read/write_data or on desc. Now that you ask for it, I think
>> following approach is possible:
>>
>> 1. remove the limit on IO_MAX at .pg_test.
>> 2. ask for layout at .pg_doio for the size of current IO desc
>> 3. if server returns short layout, split nfs_read/write_data or desc and issue the pagelist covered by lseg.
>> 4. do 2 and 3 in a loop until all pages in current desc is handled.
>>
> 
> So in effect you are doing what I suggest two passes 
> one: what's the next hole,
> second: Collect pages slicing by returned lo_seg
> 
> Don't you think it is more simple to do a 3 line preliminary
> loop in "one:"?
> 
> and keep the current code that is now exactly built to do
> "second:"
> 
> You are suggesting to effectively repeat current code using
> the first .pg_init...pg_doio for one: and hacking for blocks
> "second:"
> 
> I want 3 lines of code for one: and keep second: exactly as is.
> 
> <snip>
> 
>> Looks like you are suggesting going through the dirty page list twice
>> before issuing IO, one just for getting the IO size information and
>> another one for page collapsing. The whole point of moving layoutget
>> to .pg_doio is to collect real IO size there because we don't know it
>> at .pg_init. And it is done without any changes to generic NFS IO
>> path. I'm not sure if it is appropriate to change generic IO routine
>> to collect the information before .pg_init (I'd be happy too if we
>> can do it there).
> 
> That's what you are suggesting as well look in your step 4.:
> 	do 2 and 3 in a loop until all pages in current desc is handled
> sounds like another loop on all pages no?
> 
> BTW: we are already doing two passes in the system we already looked
> through all the pages when building the io desc at .write/read_pages
> 
> At first we can do above 3 lines loop in .pg_init. Second we can
> just collect that information in generic nfs at the first loop
> we are already doing
> 
>>>
>>>     a. We want it at .pg_init so we have a layout at .pg_test to inspect.
>>>
>>>        Done properly will let you, in blocks, slice by extents at .pg_test
>>>        and .write_pages can send the complete paglist to md (bio chaining)
>>>
>> Unlike objects and files, blocks don't slice by extents, not at .pg_test, nor at .read/write_pagelist.
>>  
> 
> What? What do you do? Send a scsi scatter list command?
> I don't think so. Somewhere you have to see an extent boundary of the data
> and send the continue of the next extent on disk as a new block request
> in a new bio with a new disk offset. No?
> 
> I'm not saying to do this right away, but you could simplify the code a lot
> by slicing by extent inside .pg_test
> 
> <>
>>>
>>>     At first version:
>>>       A good approximation which gives you an exact middle point
>>>       between blocks B.2 and objects/files B.2, is dirty count.
>>>     At later patch:
>>>       Have generic NFS collect the above O1, N1, and Nn for you and base
>>>       your decision on that.
>>>
>>
>> Well, unless you put both the two parts in... The first version is
>> ignoring the fact that blocks MDS cannot give out file stripping
>> information as easily as objects and files do. And I will stand
>> against it alone because all it does is to benefit objects while
>> hurting blocks (files don't care because they use whole file layout,
>> at least for now).
> 
> Lets make a computerize lets find O1..N1 and put in the Generic

computerize => compromise

> code for everyone objects files-segmented and blocks. Because I
> need it two. And I'd like O1..Nn but for first step I'd love
> O1..N1 a lot.
> 
> Please see my point. You created a system that only blocks can
> benefit from unless objects repeats the same exact but duplicated
> hacks as blocks.
> 
> Please do the *very* simple thing I suggest which we can all enjoy.
> 
>>
>> Otherwise, I would suggest having private hack for blocks because we have a real problem to solve.
>>
> 
> It's just as real for objects, and files when they will do segments.
> 
> My suggestion is to have two helpers at pnfs.c one for blocks and
> objects, one for files. Which can be called in .pg_init.
> The blocks/objects does a simple loop counting the first contiguous
> chunk and asks for a layout, like today. files one just sends
> all-file request.
> 
> Boaz
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

RE: [PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[tao.peng]

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by1pbmZvLmh0bWwNCg0K

Re: [PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[Boaz Harrosh]

On 12/02/2011 06:59 AM, tao.peng@emc.com wrote:
>>
> I'm sorry but I don't get it... How do you count the first contiguous
> chunk in .pg_init? All you know at .pg_init is an empty io desc and
> an nfs page. Are you going to scan the radix tree and find the next
> page that write_cache_pages is going to flush out? I don't really
> think anyone will agree on it... Please look into the second part of
> your solution and then you'll see why I am worried that it may never
> get done.> 
> Best Regards,
> Tao
> 

Rrrr, one thing I cannot do is make some one understand.

I guess I'll have to do it my self. It's so simple I'm go'ne cry.

I have more pressed things on my plate then fix broken blocks servers
but you are forcing my hands. The last code you sent is not acceptable
because it is totally not usable by objects and files (segments).

Give me a week. Not that it should take longer then an hour but
because I have burning matters to attend to first.

Boaz

>> Boaz
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

RE: [PATCH-RESEND 4/4] pnfsblock: do not ask for layout in pg_init

[tao.peng]

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