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Block layer discard requestsBlock layer discard requestsPosted Aug 14, 2008 11:22 UTC (Thu) by willy (subscriber, #9762)In reply to: Block layer discard requests by jzbiciak Parent article: Block layer discard requests
We guarantee the ordering by making discard requests be soft barriers.
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Reordering requirements Posted Aug 15, 2008 9:34 UTC (Fri) by pjm (subscriber, #2080) [Link] What am I missing? Jon Corbet's article and seanyoung's implementation and possibly willy's comment above suggest that these trim/punch/discard/... requests are somehow very special in their reordering requirements, whereas it seems to me that a discard is just the same as a write: the existing code mustn't reorder any writes to a given block, and the new code mustn't reorder any write-or-discard requests to a given block. This shouldn't require any more barriers or speed penalty than we already have for writes. (The only difference is that one might use *looser* requirements for reordering discards and reads for a given block, depending on the semantics of reading a discarded block.)
Reordering requirements Posted Aug 15, 2008 14:54 UTC (Fri) by willy (subscriber, #9762) [Link] This was already discussed in the email thread ... overlapping writes are already serialised by the page lock. Discard doesn't have a page to lock, so you can't rely on this.
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