On Thu, Jan 15, 2009 at 09:50:57PM +0530, Manish Katiyar wrote: > On Thu, Jan 15, 2009 at 7:30 PM, Matthew Wilcox <matthew@xxxxxx> wrote: > > On Thu, Jan 15, 2009 at 02:50:27PM +0100, Francis Moreau wrote: > >> Let's say that a process wants to read a page of data stored in a file. > >> For that it issues a sys_read(). > >> > >> Now the data page is not in the page cache and it must be fetched from > >> the disk. > >> > >> So I assume while the data page is recovered from the disk, the process > >> is suspended until the data are ready to be read. > >> > >> Could anybody show me where in the source code where the process is > >> suspended ? > > I might be wrong, because I am a newbie too.......but still i will > try. I think it follows the below path. > > do_generic_file_read() -> find_get_page() (This tries to find the > required page in cache). If we don't find here we try to do a > readahead using page_cache_sync_readahead() and then we eventually > call mpage_readpage() -> do_mpage_readpage() and then we put it in the > cache using add_to_page_cache_lru(). > > Please correct me if I am wrong. You're not wrong, but you aren't answering his question. He asked where the process is suspended, and the answer is "in __lock_page_killable()". > Thanks - > Manish > > > > > Sure. Take a look in mm/filemap.c. Filesystems that use the page cache > > will usually end up calling do_generic_file_read() one way or another. > > It tries to find the page in the page cache, when it doesn't find the > > page, it creates it, then calls ->readpage() to start the read, and > > lock_page_killable() to wait for the page to be read. As the comment > > says, when the read finishes, it will unlock the page and the reader > > will continue. > > > > -- > > Matthew Wilcox Intel Open Source Technology Centre > > "Bill, look, we understand that you're interested in selling us this > > operating system, but compare it to ours. We can't possibly take such > > a retrograde step." > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
