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SubjectRe: [RFC] [PATCH 2/4]delayed allocation for ext3
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On Tue, 2005-07-26 at 15:52 -0700, Andrew Morton wrote:
> Mingming Cao <cmm@us.ibm.com> wrote:
> >
> > Here is the updated patch from Badari for delayed allocation for ext3.
> > Delayed allocation defers block allocation from prepare-write time to
> > page writeout time.
>
> For data=writeback only, yes?

Yes.

>
> > ...
> > --- linux-2.6.12/fs/ext3/inode.c~ext3-delalloc 2005-07-14 23:15:34.866752480 -0700
> > +++ linux-2.6.12-ming/fs/ext3/inode.c 2005-07-14 23:15:34.889748984 -0700
> > @@ -1340,6 +1340,9 @@ static int ext3_prepare_write(struct fil
> > handle_t *handle;
> > int retries = 0;
> >
> > +
> > + if (test_opt(inode->i_sb, DELAYED_ALLOC))
> > + return __nobh_prepare_write(page, from, to, ext3_get_block, 0);
>
> Rather than performing this test on each ->prepare_write(), would it not be
> better to set up a new set of address_space_operations for this mode?
>
> __nobh_prepare_write() seems like a poor choice of name?

You are correct. I was trying to minimize the changes to interfaces.
Once we get it working, I will do it as part of cleanups.

>
> > retry:
> > handle = ext3_journal_start(inode, needed_blocks);
> > if (IS_ERR(handle)) {
> > @@ -1439,6 +1442,9 @@ static int ext3_writeback_commit_write(s
> > else
> > ret = generic_commit_write(file, page, from, to);
> >
> > + if (test_opt(inode->i_sb, DELAYED_ALLOC))
> > + return ret;
> > +
>
> Here too, perhaps.
>
> > + }
> > + }
> > /*
> > * The journal_load will have done any necessary log recovery,
> > * so we can safely mount the rest of the filesystem now.
> > diff -puN fs/buffer.c~ext3-delalloc fs/buffer.c
> > --- linux-2.6.12/fs/buffer.c~ext3-delalloc 2005-07-14 23:15:34.875751112 -0700
> > +++ linux-2.6.12-ming/fs/buffer.c 2005-07-14 23:15:34.903746856 -0700
> > @@ -2337,8 +2337,8 @@ static void end_buffer_read_nobh(struct
> > * On entry, the page is fully not uptodate.
> > * On exit the page is fully uptodate in the areas outside (from,to)
> > */
> > -int nobh_prepare_write(struct page *page, unsigned from, unsigned to,
> > - get_block_t *get_block)
> > +int __nobh_prepare_write(struct page *page, unsigned from, unsigned to,
> > + get_block_t *get_block, int create)
>
> Suggest you make this static and update the comment.
>

Sure.

> > {
> > struct inode *inode = page->mapping->host;
> > const unsigned blkbits = inode->i_blkbits;
> > @@ -2370,10 +2370,8 @@ int nobh_prepare_write(struct page *page
> > block_start < PAGE_CACHE_SIZE;
> > block_in_page++, block_start += blocksize) {
> > unsigned block_end = block_start + blocksize;
> > - int create;
> >
> > map_bh.b_state = 0;
> > - create = 1;
> > if (block_start >= to)
> > create = 0;
> > ret = get_block(inode, block_in_file + block_in_page,
>
> What's going on here? Seems that we'll call get_block() with `create=0'.
> Is there any point in doing that? For delayed allocation we shuld be able
> to skip get_block() altogether here and, err, delay it.

For delayed allocation, I need to delay the block allocation - but I
still need to do get_block(READ) and read the data from the block - if
the block already exists.

>
> > +int nobh_prepare_write(struct page *page, unsigned from, unsigned
> > + get_block_t *get_block)
> > +{
> > + return __nobh_prepare_write(page, from, to, get_block, 1);
> > +}
> > +
> > EXPORT_SYMBOL(nobh_prepare_write);
>
> Here you add nobh_dalloc_prepare_write() and remember to export it to
> modules this time ;)
>

Will do.

Thanks,
Badari

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