lkml.org 
[lkml]   [2023]   [May]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 17/17] fs: add CONFIG_BUFFER_HEAD
    On Sun, Apr 30, 2023 at 08:14:03PM -0700, Luis Chamberlain wrote:
    > On Sat, Apr 29, 2023 at 02:20:17AM +0100, Matthew Wilcox wrote:
    > > > [ 11.322212] Call Trace:
    > > > [ 11.323224] <TASK>
    > > > [ 11.324146] iomap_readpage_iter+0x96/0x300
    > > > [ 11.325694] iomap_readahead+0x174/0x2d0
    > > > [ 11.327129] read_pages+0x69/0x1f0
    > > > [ 11.329751] page_cache_ra_unbounded+0x187/0x1d0
    > >
    > > ... that shouldn't be possible. read_pages() allocates pages, puts them
    > > in the page cache and tells the filesystem to fill them in.
    > >
    > > In your patches, did you call mapping_set_large_folios() anywhere?
    >
    > No but the only place to add that would be in the block cache. Adding
    > that alone to the block cache doesn't fix the issue. The below patch
    > however does get us by.

    That's "working around the error", not fixing it ... probably the same
    root cause as your other errors; at least I'm not diving into them until
    the obvious one is fixed.

    > >From my readings it does't seem like readahead_folio() should always
    > return non-NULL, and also I couldn't easily verify the math is right.

    readahead_folio() always returns non-NULL. That's guaranteed by how
    page_cache_ra_unbounded() and page_cache_ra_order() work. It allocates
    folios, until it can't (already-present folio, ENOMEM, EOF, max batch
    size) and then calls the filesystem to make those folios uptodate,
    telling it how many folios it put in the page cache, where they start.

    Hm. The fact that it's coming from page_cache_ra_unbounded() makes
    me wonder if you updated this line:

    folio = filemap_alloc_folio(gfp_mask, 0);

    without updating this line:

    ractl->_nr_pages++;

    This is actually number of pages, not number of folios, so needs to be
    ractl->_nr_pages += 1 << order;

    various other parts of page_cache_ra_unbounded() need to be examined
    carefully for assumptions of order-0; it's never been used for that
    before. all the large folio work has concentrated on
    page_cache_ra_order()

    \
     
     \ /
      Last update: 2023-05-01 17:47    [W:4.535 / U:0.000 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site