Messages in this thread | | | Date | Mon, 1 May 2006 19:41:54 +0200 | From | Jens Axboe <> | Subject | Re: splice(SPLICE_F_MOVE) problems |
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On Mon, May 01 2006, Oleg Nesterov wrote: > On 05/01, Jens Axboe wrote: > > > > On Mon, May 01 2006, Oleg Nesterov wrote: > > > > > > I can't understand why do we need PIPE_BUF_FLAG_STOLEN at all. > > > It seems to me we need a local boolean in pipe_to_file. > > > > PIPE_BUF_FLAG_STOLEN used to be used in the release function as well, > > hence the flag. > > Ok, but in that case > > > I'll make sure to clear > > the flag as well on add_to_page_cache() failure. > > ... it is not good to clear it in pipe_to_file(). The page remains > stolen from pipe_buf_operations pov, this flag imho should be private > to buf, and page_cache_pipe_buf_ops doesn't need it. > > I think pipe_to_buf() can test 'buf->page == page' instead of > PIPE_BUF_FLAG_STOLEN.
I ended up fixing it with a local variable, but you are right it can be killed with just a buf->page != page == stolen check. I got rid of the last check of that, so just one remaining. Will commit this change.
> Another question, > > __generic_file_splice_read: > > /* > * Initiate read-ahead on this page range. however, don't call into > * read-ahead if this is a non-zero offset (we are likely doing small > * chunk splice and the page is already there) for a single page. > */ > if (!loff || nr_pages > 1) > page_cache_readahead(mapping, &in->f_ra, in, index, nr_pages); > > Why this check? page_cache_readahead() should detect sub-page > reads correctly.
Leftover from do_page_cache_readahead I suppose. I probably shouldn't try to second guess read-ahead, however.
> page = find_get_page(mapping, index); > if (!page) { > page = page_cache_alloc_cold(); > > add_to_page_cache_lru(page); > > I think it makes sense to add handle_ra_miss() here. Otherwise, > for example, readahead could be disabled by RA_FLAG_INCACHE > forever.
Good point, added.
> If readahead doesn't work, SPLICE_F_MOVE is problematic too. > add_to_page_cache_lru()->lru_cache_add() first increments > page->count and adds this page to lru_add_pvecs. This means > page_cache_pipe_buf_steal()->remove_mapping() will probably > fail.
Because of the temporarily elevated page count?
-- Jens Axboe
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