Messages in this thread | | | Subject | Re: Q: generic_file_write sets PG_locked??? | From | (Eric W. Biederman) | Date | 23 Apr 1999 20:03:58 -0500 |
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>>>>> "LT" == Linus Torvalds <torvalds@transmeta.com> writes:
LT> In article <14111.40097.154796.570022@dukat.scot.redhat.com>, LT> Stephen C. Tweedie <sct@redhat.com> wrote: >> >> Yes and no. PageLocked may just indicate a background writeback in >> progress. That definitely happens in the swap cache right now, but the >> vfs code doesn't use it for the page cache (yet). It will do.
LT> In fact, it already does for NFS, which uses PageLocked for exactly that LT> reason (to serialize read and write requests to the same page).
As I understand the NFS code it also tries using PageLocked to synchronize writes _to_ a page from user space.
>> However, >> if a given filesystem provides its own write-page strategy functions >> which have their own locking semantics, there's no real reason to >> prevent it from doing so as long as the page mapping functions continue >> to block on a non-uptodate page.
LT> For "valid to read", you only check Uptodate. For any actual IO LT> (whether it's because you're going to actually _do_ the read or set up LT> some write), PageLocked should be used to synchronize. NFS already does LT> this, and generic_file_read() already understands about it.
generic_file_read is quite close but it always does wait_on_page. Not wrong, but not necessary if the page is Uptodate.
Eric
P.S. I'm looking at 2.2.5 so I may be a hair behind.
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