On 09/01/2016 10:58 PM, Wang Xiaoguang wrote:
In btrfs_async_reclaim_metadata_space(), we use ticket's address to determine whether asynchronous metadata reclaim work is making progress.ticket = list_first_entry(&space_info->tickets, struct reserve_ticket, list); if (last_ticket == ticket) { flush_state++; } else { last_ticket = ticket; flush_state = FLUSH_DELAYED_ITEMS_NR; if (commit_cycles) commit_cycles--; } But indeed it's wrong, we should not rely on local variable's address to do this check, because addresses may be same. In my test environment, I dd one 168MB file in a 256MB fs, found that for this file, every time wait_reserve_ticket() called, local variable ticket's address is same, For above codes, assume a previous ticket's address is addrA, last_ticket is addrA. Btrfs_async_reclaim_metadata_space() finished this ticket and wake up it, then another ticket is added, but with the same address addrA, now last_ticket will be same to current ticket, then current ticket's flush work will start from current flush_state, not initial FLUSH_DELAYED_ITEMS_NR, which may result in some enospc issues(I have seen this in my test machine). Signed-off-by: Wang Xiaoguang <[email protected]>
We want to track the progress of the individual tickets, not whether or not we make progress on the space_info, so instead store the global ticket id in space_info and store the individual ticket_id in the ticket itself, and use that as the last_tickets_id. Thanks,
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