Messages in this thread Patch in this message | | | Date | Sat, 22 Dec 2007 09:31:48 +0800 | From | Fengguang Wu <> | Subject | [PATCH 1/9] readahead: simplify readahead call scheme |
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It is insane and error-prone to insist on the call sites to check for async readahead after doing any sync one. I.e. whenever someone do a sync readahead:
if (!page) page_cache_sync_readahead(...);
He must try async readahead, too:
page = find_get_page(...); if (PageReadahead(page)) page_cache_async_readahead(...);
The tricky point is that PG_readahead could be set by a sync readahead for the _current_ newly faulted in page, and the readahead code simply expects one more callback to handle it. If the caller fails to do so, it will miss the PG_readahead bits and never able to start an async readahead.
Avoid it by piggy-backing the async part _inside_ the readahead code.
Now if an async readahead should be started immediately after a sync one, the readahead logic itself will do it. So the following code becomes valid:
if (!page) page_cache_sync_readahead(...); else if (PageReadahead(page)) page_cache_async_readahead(...);
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn> --- mm/readahead.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- linux-2.6.24-rc5-mm1.orig/mm/readahead.c +++ linux-2.6.24-rc5-mm1/mm/readahead.c @@ -402,6 +402,14 @@ ondemand_readahead(struct address_space ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size; readit: + /* + * An async readahead should be triggered immediately. + * Instead of demanding all call sites to check for async readahead + * immediate after a sync one, start the async part now and here. + */ + if (!hit_readahead_marker && ra->size == ra->async_size) + ra->size *= 2; + return ra_submit(ra, mapping, filp); } --
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