Writes blocked on wait_for_stable_page (Writes of less than page size sometimes take too long)

Hi
I am working on a 64 bit Android device and have been trying to improve performance for stream based data download (for example an ftp)
The device has 3GB of ram and the dirty_ratio and dirty_background_ratio are set to 5 and 1 respectively.

Kernel 3.10 , Highmem is not enabled and the backing device is a emmc and checksumming is not enabled

I noticed when profiling writes that if we dont use streamed IO (ie. use write of whatever size data was read on the tcp stream) there are some writes that seem to get blocked on wait_for_stable_page.

If I force the writes to be buffered in the userspace and ensure writing 4k chunks the writes never seem to stall.

I noticed there was earlier discussion on this and idea were proposed to use snapshotting of the pages to avoid stalls... For example: https://lwn.net/Articles/546658/

But this seems to only snapshot ext3 ... (unless i misunderstood what the patch is doing)

Is there a similar patch to snapshot the buffers to not stall the writes for ext4?

Please let me know.

I would really appreciate any help you can give me.

Signature · 10 lines

Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Quoted 7 lines · Nikhilesh Reddy

Hi
I am working on a 64 bit Android device and have been trying to improve performance for stream based data download (for example an ftp)
The device has 3GB of ram and the dirty_ratio and dirty_background_ratio are set to 5 and 1 respectively.

Quoted 2 lines

Kernel 3.10 , Highmem is not enabled and the backing device is a emmc and checksumming is not enabled

Ok, 3.10 kernel is new enough that stable page writes only apply to devices that demand it, and apparently your eMMC demands it.

Quoted 8 lines

I noticed when profiling writes that if we dont use streamed IO (ie. use write of whatever size data was read on the tcp stream) there are some writes that seem to get blocked on wait_for_stable_page.

If I force the writes to be buffered in the userspace and ensure writing 4k chunks the writes never seem to stall.

That's consistent with a page being partially dirtied, written out, and partially dirtied again before write-out finishes. If you buffer the incoming data such that a page is only dirtied once, you'll never notice wait_for_stable_page.

Are you explicitly forcing writeout (i.e. fsync()) after every chunk arrives? Or, is the rate of incoming data high enough such that we hit either dirty*ratio limit? It isn't too hard to hit 30MB these days. Why are you lowering the ratios from their defaults?

Quoted 10 lines

I noticed there was earlier discussion on this and idea were proposed to use snapshotting of the pages to avoid stalls... For example: https://lwn.net/Articles/546658/

But this seems to only snapshot ext3 ... (unless i misunderstood what the patch is doing)

Is there a similar patch to snapshot the buffers to not stall the writes for ext4?

No, there is not -- the problem with the snapshot solution is that it requires page allocations when the FS is (potentially) trying to reclaim memory by writing out dirty pages.

--D

Quoted 16 lines

Please let me know.

I would really appreciate any help you can give me.

Signature · 10 lines

Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Hi Darrick
Thanks so much for your reply.
I apologize the stable page wait seems to be an odd outlier in that run ... I ran multiple traces again.

Please find my answers inline below.

Quoted 8 lines · Darrick J. Wong

Quoted 7 lines · Nikhilesh Reddy

Hi
I am working on a 64 bit Android device and have been trying to improve performance for stream based data download (for example an ftp)
The device has 3GB of ram and the dirty_ratio and dirty_background_ratio are set to 5 and 1 respectively.

Quoted 4 lines

Quoted 2 lines

Kernel 3.10 , Highmem is not enabled and the backing device is a emmc and checksumming is not enabled

Ok, 3.10 kernel is new enough that stable page writes only apply to devices that demand it, and apparently your eMMC demands it.

I tried checking my logs again .. and yes the stable pages dont apply ... that seems to be an odd instance where it took a while. /My apologies.

So On running many more trace runs it appears that the wait is actually on in the function

wait_on_page_writeback(page) ext4_da_write_begin

Snippet below

/*
* grab_cache_page_write_begin() can take a long time if the
* system is thrashing due to memory pressure, or if the page
* is being written back. So grab it first before we start
* the transaction handle. This also allows us to allocate
* the page (if needed) without using GFP_NOFS.
*/
retry_grab:

     page = grab_cache_page_write_begin(mapping, index, flags);
     if (!page)
         return -ENOMEM;
     unlock_page(page);

retry_journal:

     handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE, needed_blocks);
     if (IS_ERR(handle)) {
         page_cache_release(page);
         return PTR_ERR(handle);
     }

     lock_page(page);
     if (page->mapping != mapping) {
         /* The page got truncated from under us */
         unlock_page(page);
         page_cache_release(page);
         ext4_journal_stop(handle);
         goto retry_grab;
     }
     wait_on_page_writeback(page); <<<<<<<<<<<<<<<<<<This is where the

wait is!

The writeback just seems to take long.. but only when we write to the same page over again...
The grab_cache_page_write_begin gives the same page until we write enough...

Is there a wait to not wait for the writeback?

Quoted 13 lines

Quoted 8 lines

I noticed when profiling writes that if we dont use streamed IO (ie. use write of whatever size data was read on the tcp stream) there are some writes that seem to get blocked on wait_for_stable_page.

If I force the writes to be buffered in the userspace and ensure writing 4k chunks the writes never seem to stall.

That's consistent with a page being partially dirtied, written out, and partially dirtied again before write-out finishes. If you buffer the incoming data such that a page is only dirtied once, you'll never notice wait_for_stable_page.

Quoted 4 lines

Are you explicitly forcing writeout (i.e. fsync()) after every chunk arrives? Or, is the rate of incoming data high enough such that we hit either dirty*ratio limit? It isn't too hard to hit 30MB these days. Why are you lowering the ratios from their defaults?

Using the higher values seems to cause longer stall ...when we do stall... Smaller values are cause the write out to happen often but each one takes less time.

Setting it to the defaults causes a longer stall which seems to be impacting TCP due to the delay in reading.
Additional info : dirty_expire_centisecs was set to 200 and the data rate is close to 300Mbps. so yea 30MB should be less than a second.

Am I missing something obvious here?

Please do let me know.

Thanks so much for you help

Quoted 33 lines

Quoted 10 lines

I noticed there was earlier discussion on this and idea were proposed to use snapshotting of the pages to avoid stalls... For example: https://lwn.net/Articles/546658/

But this seems to only snapshot ext3 ... (unless i misunderstood what the patch is doing)

Is there a similar patch to snapshot the buffers to not stall the writes for ext4?

No, there is not -- the problem with the snapshot solution is that it requires page allocations when the FS is (potentially) trying to reclaim memory by writing out dirty pages.

--D

Quoted 17 lines

Please let me know.

I would really appreciate any help you can give me.

--
Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html

Also can someone please confirm if the following patch help address this issue That I described below?

https://kernel.googlesource.com/pub/scm/linux/kernel/git/tytso/ext4/+/7afe5aa59ed3da7b6161617e7f157c7c680dc41e

Quick Summary:

in the function
wait_on_page_writeback(page) inside ext4_da_write_begin seems to take long and the process is stuck waiting.

The writeback just seems to take long.. but only when we write to the same page over again...
The grab_cache_page_write_begin gives the same page until we write enough...
Is there a wait to not wait for the writeback?

Quoted 90 lines

Hi Darrick
Thanks so much for your reply.
I apologize the stable page wait seems to be an odd outlier in that run ... I ran multiple traces again.

Please find my answers inline below.

Quoted 8 lines · Darrick J. Wong

Quoted 7 lines · Nikhilesh Reddy

Hi
I am working on a 64 bit Android device and have been trying to improve performance for stream based data download (for example an ftp)
The device has 3GB of ram and the dirty_ratio and dirty_background_ratio are set to 5 and 1 respectively.

Quoted 4 lines

Quoted 2 lines

Kernel 3.10 , Highmem is not enabled and the backing device is a emmc and checksumming is not enabled

Ok, 3.10 kernel is new enough that stable page writes only apply to devices that demand it, and apparently your eMMC demands it.

I tried checking my logs again .. and yes the stable pages dont apply ... that seems to be an odd instance where it took a while. /My apologies.

So On running many more trace runs it appears that the wait is actually on in the function

wait_on_page_writeback(page) ext4_da_write_begin

Snippet below

/*
* grab_cache_page_write_begin() can take a long time if the
* system is thrashing due to memory pressure, or if the page
* is being written back. So grab it first before we start
* the transaction handle. This also allows us to allocate
* the page (if needed) without using GFP_NOFS.
*/
retry_grab:

    page = grab_cache_page_write_begin(mapping, index, flags);
    if (!page)
        return -ENOMEM;
    unlock_page(page);

retry_journal:

    handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE, needed_blocks);
    if (IS_ERR(handle)) {
        page_cache_release(page);
        return PTR_ERR(handle);
    }

    lock_page(page);
    if (page->mapping != mapping) {
        /* The page got truncated from under us */
        unlock_page(page);
        page_cache_release(page);
        ext4_journal_stop(handle);
        goto retry_grab;
    }
    wait_on_page_writeback(page); <<<<<<<<<<<<<<<<<<This is where the

wait is!

The writeback just seems to take long.. but only when we write to the same page over again...
The grab_cache_page_write_begin gives the same page until we write enough...

Is there a wait to not wait for the writeback?

Quoted 17 lines

Quoted 8 lines

I noticed when profiling writes that if we dont use streamed IO (ie. use write of whatever size data was read on the tcp stream) there are some writes that seem to get blocked on wait_for_stable_page.

If I force the writes to be buffered in the userspace and ensure writing 4k chunks the writes never seem to stall.

That's consistent with a page being partially dirtied, written out, and partially dirtied again before write-out finishes. If you buffer the incoming data such that a page is only dirtied once, you'll never notice wait_for_stable_page.

Are you explicitly forcing writeout (i.e. fsync()) after every chunk arrives? Or, is the rate of incoming data high enough such that we hit either dirty*ratio limit? It isn't too hard to hit 30MB these days. Why are you lowering the ratios from their defaults?

Quoted 8 lines

Using the higher values seems to cause longer stall ...when we do stall... Smaller values are cause the write out to happen often but each one takes less time.

Setting it to the defaults causes a longer stall which seems to be impacting TCP due to the delay in reading.
Additional info : dirty_expire_centisecs was set to 200 and the data rate is close to 300Mbps. so yea 30MB should be less than a second.

Quoted 43 lines

Am I missing something obvious here?

Please do let me know.

Thanks so much for you help

Quoted 33 lines

Quoted 10 lines

I noticed there was earlier discussion on this and idea were proposed to use snapshotting of the pages to avoid stalls... For example: https://lwn.net/Articles/546658/

But this seems to only snapshot ext3 ... (unless i misunderstood what the patch is doing)

Is there a similar patch to snapshot the buffers to not stall the writes for ext4?

No, there is not -- the problem with the snapshot solution is that it requires page allocations when the FS is (potentially) trying to reclaim memory by writing out dirty pages.

--D

Quoted 17 lines

Please let me know.

I would really appreciate any help you can give me.

--
Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html

Signature · 6 lines

Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

Quoted 11 lines · Nikhilesh Reddy

Also can someone please confirm if the following patch help address this issue That I described below?

https://kernel.googlesource.com/pub/scm/linux/kernel/git/tytso/ext4/+/7afe5aa59ed3da7b6161617e7f157c7c680dc41e

Quick Summary:

in the function
wait_on_page_writeback(page) inside ext4_da_write_begin seems to take long and the process is stuck waiting.

Quoted 5 lines

The writeback just seems to take long.. but only when we write to the same page over again...
The grab_cache_page_write_begin gives the same page until we write enough...
Is there a wait to not wait for the writeback?

Oh, right. <smacks head>

Yes, that wait_for_page_writeback() was replaced with a call to wait_for_stable_page() upstream, so it'll probably work for your 3.10 kernel.

(I also wonder why not jump to a newer LTS kernel, but that's neither here nor there.)

<more below>

Quoted 92 lines · Nikhilesh Reddy

Quoted 90 lines

Hi Darrick
Thanks so much for your reply.
I apologize the stable page wait seems to be an odd outlier in that run ... I ran multiple traces again.

Please find my answers inline below.

Quoted 8 lines · Darrick J. Wong

Quoted 7 lines · Nikhilesh Reddy

Hi
I am working on a 64 bit Android device and have been trying to improve performance for stream based data download (for example an ftp)
The device has 3GB of ram and the dirty_ratio and dirty_background_ratio are set to 5 and 1 respectively.

Quoted 4 lines

Quoted 2 lines

Kernel 3.10 , Highmem is not enabled and the backing device is a emmc and checksumming is not enabled

Ok, 3.10 kernel is new enough that stable page writes only apply to devices that demand it, and apparently your eMMC demands it.

I tried checking my logs again .. and yes the stable pages dont apply ... that seems to be an odd instance where it took a while. /My apologies.

So On running many more trace runs it appears that the wait is actually on in the function

wait_on_page_writeback(page) ext4_da_write_begin

Snippet below

/*
* grab_cache_page_write_begin() can take a long time if the
* system is thrashing due to memory pressure, or if the page
* is being written back. So grab it first before we start
* the transaction handle. This also allows us to allocate
* the page (if needed) without using GFP_NOFS.
*/
retry_grab:

     page = grab_cache_page_write_begin(mapping, index, flags);
     if (!page)
         return -ENOMEM;
     unlock_page(page);

retry_journal:

     handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE, needed_blocks);
     if (IS_ERR(handle)) {
         page_cache_release(page);
         return PTR_ERR(handle);
     }

     lock_page(page);
     if (page->mapping != mapping) {
         /* The page got truncated from under us */
         unlock_page(page);
         page_cache_release(page);
         ext4_journal_stop(handle);
         goto retry_grab;
     }
     wait_on_page_writeback(page); <<<<<<<<<<<<<<<<<<This is where the

wait is!

The writeback just seems to take long.. but only when we write to the same page over again...
The grab_cache_page_write_begin gives the same page until we write enough...

Is there a wait to not wait for the writeback?

Quoted 17 lines

Quoted 8 lines

I noticed when profiling writes that if we dont use streamed IO (ie. use write of whatever size data was read on the tcp stream) there are some writes that seem to get blocked on wait_for_stable_page.

If I force the writes to be buffered in the userspace and ensure writing 4k chunks the writes never seem to stall.

That's consistent with a page being partially dirtied, written out, and partially dirtied again before write-out finishes. If you buffer the incoming data such that a page is only dirtied once, you'll never notice wait_for_stable_page.

Are you explicitly forcing writeout (i.e. fsync()) after every chunk arrives? Or, is the rate of incoming data high enough such that we hit either dirty*ratio limit? It isn't too hard to hit 30MB these days. Why are you lowering the ratios from their defaults?

Quoted 8 lines

Quoted 8 lines

Using the higher values seems to cause longer stall ...when we do stall... Smaller values are cause the write out to happen often but each one takes less time.

Setting it to the defaults causes a longer stall which seems to be impacting TCP due to the delay in reading.
Additional info : dirty_expire_centisecs was set to 200 and the data rate is close to 300Mbps. so yea 30MB should be less than a second.

Ah, you're concerned about the writeout latency, and it's important that incoming data end up on flash as quickly as is convenient. Hm.

That patch you found will probably get rid of the symptoms; I'd also suggest fsync()ing after each page boundary instead of lowering the writeback ratios since that increases the write load systemwide, which will make the writeouts for your app take more time and wear out the flash sooner.

--D

Quoted 52 lines

Quoted 43 lines

Am I missing something obvious here?

Please do let me know.

Thanks so much for you help

Quoted 33 lines

Quoted 10 lines

I noticed there was earlier discussion on this and idea were proposed to use snapshotting of the pages to avoid stalls... For example: https://lwn.net/Articles/546658/

But this seems to only snapshot ext3 ... (unless i misunderstood what the patch is doing)

Is there a similar patch to snapshot the buffers to not stall the writes for ext4?

No, there is not -- the problem with the snapshot solution is that it requires page allocations when the FS is (potentially) trying to reclaim memory by writing out dirty pages.

--D

Quoted 17 lines

Please let me know.

I would really appreciate any help you can give me.

--
Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html

--
Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

Thanks so much Darrick for all your help.
That patch helped.

I had a bit of a query with respect to stable pages though...

From what I understand only backing devices that need some sort of checksumming seem to need stable pages... AS in regular emmc shouldnt need it correct?

If not then the below patch would now cause a pass-through rather than wait for writeback and I was wondering if that could cause corruptions when the same page is dirtied again with writeback in progress.

Also with respect to the flush... since the applications are prettymuch third party I cant really do much there...

But I was wondering now that there is no contention with the pages after the patch ... if reducing the cache may actually be bad.

Still running metrics so wont know until they are done.

Quoted 193 lines · Nikhilesh Reddy

Quoted 11 lines

Also can someone please confirm if the following patch help address this issue That I described below?

https://kernel.googlesource.com/pub/scm/linux/kernel/git/tytso/ext4/+/7afe5aa59ed3da7b6161617e7f157c7c680dc41e

Quick Summary:

in the function
wait_on_page_writeback(page) inside ext4_da_write_begin seems to take long and the process is stuck waiting.

Quoted 5 lines

The writeback just seems to take long.. but only when we write to the same page over again...
The grab_cache_page_write_begin gives the same page until we write enough...
Is there a wait to not wait for the writeback?

Oh, right. <smacks head>

Yes, that wait_for_page_writeback() was replaced with a call to wait_for_stable_page() upstream, so it'll probably work for your 3.10 kernel.

(I also wonder why not jump to a newer LTS kernel, but that's neither here nor there.)

<more below>

Quoted 92 lines · Nikhilesh Reddy

Quoted 90 lines

Hi Darrick
Thanks so much for your reply.
I apologize the stable page wait seems to be an odd outlier in that run ... I ran multiple traces again.

Please find my answers inline below.

Quoted 8 lines · Darrick J. Wong

Quoted 7 lines · Nikhilesh Reddy

Hi
I am working on a 64 bit Android device and have been trying to improve performance for stream based data download (for example an ftp)
The device has 3GB of ram and the dirty_ratio and dirty_background_ratio are set to 5 and 1 respectively.

Quoted 4 lines

Quoted 2 lines

Kernel 3.10 , Highmem is not enabled and the backing device is a emmc and checksumming is not enabled

Ok, 3.10 kernel is new enough that stable page writes only apply to devices that demand it, and apparently your eMMC demands it.

I tried checking my logs again .. and yes the stable pages dont apply ... that seems to be an odd instance where it took a while. /My apologies.

So On running many more trace runs it appears that the wait is actually on in the function

wait_on_page_writeback(page) ext4_da_write_begin

Snippet below

/*
* grab_cache_page_write_begin() can take a long time if the
* system is thrashing due to memory pressure, or if the page
* is being written back. So grab it first before we start
* the transaction handle. This also allows us to allocate
* the page (if needed) without using GFP_NOFS.
*/
retry_grab:

    page = grab_cache_page_write_begin(mapping, index, flags);
    if (!page)
        return -ENOMEM;
    unlock_page(page);

retry_journal:

    handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE, needed_blocks);
    if (IS_ERR(handle)) {
        page_cache_release(page);
        return PTR_ERR(handle);
    }

    lock_page(page);
    if (page->mapping != mapping) {
        /* The page got truncated from under us */
        unlock_page(page);
        page_cache_release(page);
        ext4_journal_stop(handle);
        goto retry_grab;
    }
    wait_on_page_writeback(page); <<<<<<<<<<<<<<<<<<This is where the

wait is!

The writeback just seems to take long.. but only when we write to the same page over again...
The grab_cache_page_write_begin gives the same page until we write enough...

Is there a wait to not wait for the writeback?

Quoted 17 lines

Quoted 8 lines

I noticed when profiling writes that if we dont use streamed IO (ie. use write of whatever size data was read on the tcp stream) there are some writes that seem to get blocked on wait_for_stable_page.

If I force the writes to be buffered in the userspace and ensure writing 4k chunks the writes never seem to stall.

That's consistent with a page being partially dirtied, written out, and partially dirtied again before write-out finishes. If you buffer the incoming data such that a page is only dirtied once, you'll never notice wait_for_stable_page.

Are you explicitly forcing writeout (i.e. fsync()) after every chunk arrives? Or, is the rate of incoming data high enough such that we hit either dirty*ratio limit? It isn't too hard to hit 30MB these days. Why are you lowering the ratios from their defaults?

Quoted 8 lines

Quoted 8 lines

Using the higher values seems to cause longer stall ...when we do stall... Smaller values are cause the write out to happen often but each one takes less time.

Setting it to the defaults causes a longer stall which seems to be impacting TCP due to the delay in reading.
Additional info : dirty_expire_centisecs was set to 200 and the data rate is close to 300Mbps. so yea 30MB should be less than a second.

Ah, you're concerned about the writeout latency, and it's important that incoming data end up on flash as quickly as is convenient. Hm.

That patch you found will probably get rid of the symptoms; I'd also suggest fsync()ing after each page boundary instead of lowering the writeback ratios since that increases the write load systemwide, which will make the writeouts for your app take more time and wear out the flash sooner.

--D

Quoted 52 lines

Quoted 43 lines

Am I missing something obvious here?

Please do let me know.

Thanks so much for you help

Quoted 33 lines

Quoted 10 lines

I noticed there was earlier discussion on this and idea were proposed to use snapshotting of the pages to avoid stalls... For example: https://lwn.net/Articles/546658/

But this seems to only snapshot ext3 ... (unless i misunderstood what the patch is doing)

Is there a similar patch to snapshot the buffers to not stall the writes for ext4?

No, there is not -- the problem with the snapshot solution is that it requires page allocations when the FS is (potentially) trying to reclaim memory by writing out dirty pages.

--D

Quoted 17 lines

Please let me know.

I would really appreciate any help you can give me.

--
Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html

--
Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

Signature · 6 lines

Thanks
Nikhilesh Reddy

Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

Yes, that wait_for_page_writeback() was replaced with a call to wait_for_stable_page() upstream, so it'll probably work for your 3.10 kernel.

(I also wonder why not jump to a newer LTS kernel, but that's neither here nor there.)

Quoted 6 lines · Darrick J. Wong

Yes, that wait_for_page_writeback() was replaced with a call to wait_for_stable_page() upstream, so it'll probably work for your 3.10 kernel.

(I also wonder why not jump to a newer LTS kernel, but that's neither here nor there.)

Nikhilesh said that he was using a 64-bit android device. I'm going to guess it is based off of the AOSP kernel for the Nexus 9, which is a 64-bit android device that uses 3.10 as a base. It's not *really* a 3.10 kernel, though, becausre it looks like bits and pieces of the VFS was forward ported to a somewhat newer version so they could backport F2FS to the Nexus 9 kernel. But I'm guessing he's using it because there are device drivers he needs that might not be available without a lot of forward-porting work on a newer kernel.

If you are interested in trying to use a somewhat newer version of ext4, I just *happen* to have a backport of the 3.18 version of ext4 on top of a stock version of 3.10. You can find it at the backport-to-3.10 branch of the ext4.git tree on git.kernel.org.

If you are starting from the AOSP version of the Nexus 9 kernel, the patch series from that branch won't apply 100% cleanly, because of the changes resulting from the F2FS backport. It's relatively straight-forward though to use the backport-to-3.10 patch series as a model to get a version of 3.18 ext4 on top of the AOSP kernel, though; it's mostly dropping or reworking patches that were no longer necessary thanks to the F2FS backport.

If there is interest, I can look into what might be involved in making a git repo of an AOSP kernel with the 3.18 ext4 code backported to it available.

I won't give any warrantees, of course, since the AOSP kernel doesn't build on x86 and so I can't easily run regression tests on it. So if it breaks, you will get to keep both pieces. I will try to at least look at bug reports, though, and I can say that 3.18 backport on the stock 3.10 kernel survives xfstests much better than the 3.10 version of ext4, since a modern xfstests very quickly caused the stock 3.10 kernel to panic. :-)

- Ted

Quoted 8 lines

I won't give any warrantees, of course, since the AOSP kernel doesn't build on x86 and so I can't easily run regression tests on it. So if it breaks, you will get to keep both pieces. I will try to at least look at bug reports, though, and I can say that 3.18 backport on the stock 3.10 kernel survives xfstests much better than the 3.10 version of ext4, since a modern xfstests very quickly caused the stock 3.10 kernel to panic. :-)