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Date:   Sat, 3 Oct 2020 00:49:05 -0400
From:   "Theodore Y. Ts'o" <>
To:     Ritesh Harjani <>
Subject: Re: [PATCHv3 1/1] ext4: Optimize file overwrites

On Fri, Sep 18, 2020 at 10:36:35AM +0530, Ritesh Harjani wrote:
> In case if the file already has underlying blocks/extents allocated
> then we don't need to start a journal txn and can directly return
> the underlying mapping. Currently ext4_iomap_begin() is used by
> both DAX & DIO path. We can check if the write request is an
> overwrite & then directly return the mapping information.
> This could give a significant perf boost for multi-threaded writes
> specially random overwrites.
> On PPC64 VM with simulated pmem(DAX) device, ~10x perf improvement
> could be seen in random writes (overwrite). Also bcoz this optimizes
> away the spinlock contention during jbd2 slab cache allocation
> (jbd2_journal_handle). On x86 VM, ~2x perf improvement was observed.
> Reported-by: Dan Williams <>
> Suggested-by: Jan Kara <>
> Signed-off-by: Ritesh Harjani <>

Thanks, applied.

					- Ted

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