Re: Warning on memory offline (possible in migration ?) - Kernel

This is a discussion on Re: Warning on memory offline (possible in migration ?) - Kernel ; On Thu, 17 Apr 2008 09:19:30 +0900 KAMEZAWA Hiroyuki wrote: > > I'd expect that you could reproduce this by disabling readahead with > > fadvise(POSIX_FADV_RANDOM) and then issuing the above four reads. > > > Thank you for advice. ...

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Thread: Re: Warning on memory offline (possible in migration ?)

  1. Re: Warning on memory offline (possible in migration ?)

    On Thu, 17 Apr 2008 09:19:30 +0900
    KAMEZAWA Hiroyuki wrote:
    > > I'd expect that you could reproduce this by disabling readahead with
    > > fadvise(POSIX_FADV_RANDOM) and then issuing the above four reads.
    > >

    > Thank you for advice. I'll try.
    >

    (Added lkml to CC

    What happens:
    When I do memory offline on ia64/NUMA box, __set_page_dirty_buffers() printed
    out WARNINGS because the page under migration is not up-to-date.

    Following is my investigation.

    Assume 16k pages / 4 buffers of 4096bytes block (ext3).
    4 buffers on a page of ext3.

    At page offlining, we can find a page which is not up-to-date.
    But all buffers of the page seems up-to-date.

    buffers on a page by prink().
    buffer 0, block_nr= some vaule, state= BH_uptodate | BH_Req| BH_Mapped
    buffer 1, block_nr= -1, state= BH_uptodate
    buffer 2, block_nr= -1, state= BH_uptodate
    buffer 3, block_nr= -1, state= BH_uptodate

    It seems no I/O for 3 buffers. It's because the page is the last page of inode
    and blocks for buffer[1,2,3] is not assgined.
    (maybe BH_uptodate is set by block_write_full_page().

    Adding below check can hide the warning....but I can't say this is correct.
    Can we set this page dirty silently in this case ?

    ===
    +
    +static int check_fragment_page(struct page *page, struct address_space *mapping
    )
    +{
    + struct inode *inode = mapping->host;
    + unsigned long lastblock, coverblock;
    +
    + if (!page_has_buffers(page))
    + return 0;
    +
    + lastblock = (i_size_read(inode) - 1) >> inode->i_blkbits;
    + coverblock = (page->index + 1) << (PAGE_SHIFT - inode->i_blkbits);
    +
    + return coverblock > lastblock;
    +}
    +
    +
    +
    static int __set_page_dirty(struct page *page,
    struct address_space *mapping, int warn)
    {
    @@ -717,7 +734,9 @@ static int __set_page_dirty(struct page

    write_lock_irq(&mapping->tree_lock);
    if (page->mapping) { /* Race with truncate? */
    - WARN_ON_ONCE(warn && !PageUptodate(page));
    + WARN_ON_ONCE(warn
    + && !PageUptodate(page)
    + && !check_fragment_page(page, mapping));

    if (mapping_cap_account_dirty(mapping)) {
    __inc_zone_page_state(page, NR_FILE_DIRTY);
    ==

    Thanks,
    -Kame

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  2. Re: Warning on memory offline (possible in migration ?)

    On Thu, 17 Apr 2008 15:38:18 +0900 KAMEZAWA Hiroyuki wrote:

    > On Thu, 17 Apr 2008 09:19:30 +0900
    > KAMEZAWA Hiroyuki wrote:
    > > > I'd expect that you could reproduce this by disabling readahead with
    > > > fadvise(POSIX_FADV_RANDOM) and then issuing the above four reads.
    > > >

    > > Thank you for advice. I'll try.
    > >

    > (Added lkml to CC
    >
    > What happens:
    > When I do memory offline on ia64/NUMA box, __set_page_dirty_buffers() printed
    > out WARNINGS because the page under migration is not up-to-date.


    The warning is in __set_page_dirty().

    > Following is my investigation.
    >
    > Assume 16k pages / 4 buffers of 4096bytes block (ext3).
    > 4 buffers on a page of ext3.
    >
    > At page offlining, we can find a page which is not up-to-date.
    > But all buffers of the page seems up-to-date.
    >
    > buffers on a page by prink().
    > buffer 0, block_nr= some vaule, state= BH_uptodate | BH_Req| BH_Mapped
    > buffer 1, block_nr= -1, state= BH_uptodate
    > buffer 2, block_nr= -1, state= BH_uptodate
    > buffer 3, block_nr= -1, state= BH_uptodate
    >
    > It seems no I/O for 3 buffers. It's because the page is the last page of inode
    > and blocks for buffer[1,2,3] is not assgined.
    > (maybe BH_uptodate is set by block_write_full_page().
    >
    > Adding below check can hide the warning....but I can't say this is correct.
    > Can we set this page dirty silently in this case ?
    >
    > ===
    > +
    > +static int check_fragment_page(struct page *page, struct address_space *mapping
    > )
    > +{
    > + struct inode *inode = mapping->host;
    > + unsigned long lastblock, coverblock;
    > +
    > + if (!page_has_buffers(page))
    > + return 0;
    > +
    > + lastblock = (i_size_read(inode) - 1) >> inode->i_blkbits;
    > + coverblock = (page->index + 1) << (PAGE_SHIFT - inode->i_blkbits);
    > +
    > + return coverblock > lastblock;
    > +}
    > +
    > +
    > +
    > static int __set_page_dirty(struct page *page,
    > struct address_space *mapping, int warn)
    > {
    > @@ -717,7 +734,9 @@ static int __set_page_dirty(struct page
    >
    > write_lock_irq(&mapping->tree_lock);
    > if (page->mapping) { /* Race with truncate? */
    > - WARN_ON_ONCE(warn && !PageUptodate(page));
    > + WARN_ON_ONCE(warn
    > + && !PageUptodate(page)
    > + && !check_fragment_page(page, mapping));
    >
    > if (mapping_cap_account_dirty(mapping)) {
    > __inc_zone_page_state(page, NR_FILE_DIRTY);
    > ==


    The warning is just wrong, I think. We don't nowmally hit it because
    write() will use mark_buffer_dirty() which supresses the warning and mmaped
    pages are uptodate.

    Nick?
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  3. Re: Warning on memory offline (possible in migration ?)

    On Wed, 16 Apr 2008 23:43:03 -0700
    Andrew Morton wrote:

    > On Thu, 17 Apr 2008 15:38:18 +0900 KAMEZAWA Hiroyuki wrote:
    >
    > > On Thu, 17 Apr 2008 09:19:30 +0900
    > > KAMEZAWA Hiroyuki wrote:
    > > > > I'd expect that you could reproduce this by disabling readahead with
    > > > > fadvise(POSIX_FADV_RANDOM) and then issuing the above four reads.
    > > > >
    > > > Thank you for advice. I'll try.
    > > >

    > > (Added lkml to CC
    > >
    > > What happens:
    > > When I do memory offline on ia64/NUMA box, __set_page_dirty_buffers() printed
    > > out WARNINGS because the page under migration is not up-to-date.

    >
    > The warning is in __set_page_dirty().
    >

    Sorry, __set_page_dirty() in fs/buffer.c

    Thanks,
    -Kame

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