Messages in this thread | | | Date | Wed, 25 Oct 2000 12:52:35 -0200 (BRDT) | From | Rik van Riel <> | Subject | Re: [potential bug] generic_file_readahead() |
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On Wed, 25 Oct 2000, Alexander Viro wrote:
> In generic_file_readahead(): > > unsigned long end_index = inode->i_size >> PAGE_CACHE_SHIFT; > unsigned long index = page->index; > ... > max_ahead = 0; > ... > raend = index; > if (raend < end_index) > max_ahead = filp->f_ramax; > and later > ahead = 0; > while (ahead < max_ahead) { > ahead ++; > if ((raend + ahead) >= end_index) > break; > if (page_cache_read(filp, raend + ahead) < 0) > break; > } > > AFAICS it means that we have off-by-partial here - if the file size is not > a multiple of PAGE_CACHE_SIZE we are missing the last page. Proposed > fix: > make end_index = (inode->i_size + PAGE_CACHE_SIZE - 1)>>PAGE_CACHE_SHIFT; > > Objections?
Indeed, this should fix another inefficiency in the readahead code. I'll prepare a patch for filemap.c soon (also containing ANOTHER small fix to the readahead code).
> PS: folks, could those who wrote that function comment on the > readahead rules in general? This stuff looks really ugly > (presumably from the layers and layers of small modifications) > and comments on _intentions_ of that code (as opposed to "what > are we doing in the next two lines") would be very welcome.
While I haven't written it, I'll try to come up with some documentation when I have the time (yeah right). Oh well, I'll try to at least comment on everything _I_ try to change in the kernel ;)
regards,
Rik -- "What you're running that piece of shit Gnome?!?!" -- Miguel de Icaza, UKUUG 2000
http://www.conectiva.com/ http://www.surriel.com/
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