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Re: system crash when much disk io
Neal H Walfield
Re: system crash when much disk io
Sat, 24 Nov 2001 16:39:39 +0100
Gnus/5.090004 (Oort Gnus v0.04) Emacs/21.1
> Running dselect or apt-get very often gets my hurd box on it's knees.
> When it's 'Reading Package Lists...' , the system hangs, after giving:
> ext2fs.static: ../../ext2fs/pager.c:396: file_pager_write_page:
> Assertion `block' failed.
This is a bug. I have attached a patch. Could you give it a try and
see if the bug shows up again (I have never actually seen it on my
The problem that I see is that file_pager_read_page and
file_pager_write_page both use use find_block (note: they are the only
callers of find_block) to map a page in a file to its corresponding
block on disk, however, they expect conflicting behaviors in the case
where the block is unallocated.
The find_block function does the right thing for file_pager_read_page:
when reading a page, there is no reason to have to allocate a
corresponding page on disk -- unallocated pages are just zero pages so
we make the optimization. Thus, find_block correctly calls
ext2fs_getblk with the create flag set to zero.
In the case of file_pager_write_page, unallocated pages need to be
allocated on disk: we are about to write into the region. The
file_pager_write_page function assumes that find_block will make sure
that a corresponding page exists or that it will return an error.
This is not, however, how find_block works nor should this behavior be
expected: the comment is quite clear.
My solution is to add another argument to find_block, CREATE, to
indicate how unallocated blocks should be handled.
2001-11-24 Neal H Walfield <address@hidden>
* pager.c (find_block): Take a new argument, CREATE. Pass
this to ext2_getblk instead of assuming that the callee never
wants the indicated block block to be allocated.
(file_pager_read_page): Conform to the new semantics of
> As a workaround, I tried importing /var/lib/apt/ and /var/lib/dpkg via
> nfs. However, this gives different problems: apt complains about
> E: Couldn't make mmap of 6291457 bytes - mmap (1073741869 Operation not
> E: The package lists or status file could not be parsed or opened.
The nfs client does not support mmap. I referrer you to:
RCS file: /cvsroot/hurd/hurd/ext2fs/pager.c,v
retrieving revision 1.68
diff -p -u -2 -r1.68 pager.c
--- pager.c 2001/01/07 17:03:55 1.68
+++ pager.c 2001/11/24 14:27:32
@@ -1,5 +1,5 @@
/* Pager for ext2fs
- Copyright (C) 1994,95,96,97,98,99,2000 Free Software Foundation, Inc.
+ Copyright (C) 1994,95,96,97,98,99,2000,01 Free Software Foundation, Inc.
Converted for ext2fs by Miles Bader <address@hidden>
@@ -122,11 +123,13 @@ free_page_buf (void *buf)
/* Find the location on disk of page OFFSET in NODE. Return the disk block
- in BLOCK (if unallocated, then return 0). If *LOCK is 0, then it a reader
- lock is aquired on NODE's ALLOC_LOCK before doing anything, and left
- locked after return -- even if an error is returned. 0 on success or an
- error code otherwise is returned. */
+ in BLOCK (if unallocated and CREATE is false, return 0; if
+ unallocated and CREATE is true, attempt to allocate a block). If
+ *LOCK is 0, then a reader lock is aquired on NODE's ALLOC_LOCK
+ before doing anything, and left locked after return -- even if an
+ error is returned. 0 is returned on success otherwise, an error
+ code. */
find_block (struct node *node, vm_offset_t offset,
- block_t *block, struct rwlock **lock)
+ block_t *block, int create, struct rwlock **lock)
@@ -137,9 +140,9 @@ find_block (struct node *node, vm_offset
if (offset + block_size > node->allocsize)
- err = ext2_getblk (node, offset >> log2_block_size, 0, block);
+ err = ext2_getblk (node, offset >> log2_block_size, create, block);
if (err == EINVAL)
/* Don't barf yet if the node is unallocated. */
@@ -234,5 +237,5 @@ file_pager_read_page (struct node *node,
- err = find_block (node, page, &block, &lock);
+ err = find_block (node, page, &block, 0, &lock);
@@ -391,5 +395,5 @@ file_pager_write_page (struct node *node
while (left > 0)
- err = find_block (node, offset, &block, &lock);
+ err = find_block (node, offset, &block, 1, &lock);
- Re: system crash when much disk io,
Neal H Walfield <=