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Date: Wed, 20 May 2020 08:40:39 +0000 From: Alex Zhuravlev <azhuravlev@...mcloud.com> To: Andreas Dilger <adilger@...ger.ca> CC: Alex Zhuravlev <azhuravlev@...mcloud.com>, Ritesh Harjani <riteshh@...ux.ibm.com>, "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org> Subject: Re: [PATCH 2/2] ext4: skip non-loaded groups at cr=0/1 > On 17 May 2020, at 10:55, Andreas Dilger <adilger@...ger.ca> wrote: > > The question is whether this is situation is affecting only a few inode > allocations for a short time after mount, or does this persist for a long > time? I think that it _should_ be only a short time, because these other > threads should all start prefetch on their preferred groups, so even if a > few inodes have their blocks allocated in the "wrong" group, it shouldn't > be a long term problem since the prefetched bitmaps will finish loading > and allow the blocks to be allocated, or skipped if group is fragmented. Yes, that’s the idea - there is a short window when buddy data is being populated. And for each “cluster” (not just a single group) prefetching will be initiated by allocation. It’s possible that some number of inodes will get “bad” blocks right after after mount. If you think this is a bad scenario I can introduce couple more things: 1) few times discussed prefetching thread 2) let mballoc wait for the goal group to get ready - this essentials one more check in ext4_mb_good_group() Thanks, Alex
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