Re: [RFCv5 4/5] iomap: Allocate iop in ->write_begin() early

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Matthew Wilcox <willy@xxxxxxxxxxxxx> writes:

> On Fri, May 19, 2023 at 08:48:37PM +0530, Ritesh Harjani wrote:
>> Christoph Hellwig <hch@xxxxxxxxxxxxx> writes:
>>
>> > On Mon, May 08, 2023 at 12:57:59AM +0530, Ritesh Harjani (IBM) wrote:
>> >> Earlier when the folio is uptodate, we only allocate iop at writeback
>> >
>> > s/Earlier/Currently/ ?
>> >
>> >> time (in iomap_writepage_map()). This is ok until now, but when we are
>> >> going to add support for per-block dirty state bitmap in iop, this
>> >> could cause some performance degradation. The reason is that if we don't
>> >> allocate iop during ->write_begin(), then we will never mark the
>> >> necessary dirty bits in ->write_end() call. And we will have to mark all
>> >> the bits as dirty at the writeback time, that could cause the same write
>> >> amplification and performance problems as it is now.
>> >>
>> >> However, for all the writes with (pos, len) which completely overlaps
>> >> the given folio, there is no need to allocate an iop during
>> >> ->write_begin(). So skip those cases.
>> >
>> > This reads a bit backwards, I'd suggest to mention early
>> > allocation only happens for sub-page writes before going into the
>> > details.
>> >
>>
>> sub-page is a bit confusing here. Because we can have a large folio too
>> with blocks within that folio. So we decided to go with per-block
>> terminology [1].
>>
>> [1]: https://lore.kernel.org/linux-xfs/ZFR%2FGuVca5nFlLYF@xxxxxxxxxxxxxxxxxxxx/
>>
>> I am guessing you would like to me to re-write the above para. Is this better?
>>
>> "We dont need to allocate an iop in ->write_begin() for writes where the
>> position and length completely overlap with the given folio.
>> Therefore, such cases are skipped."
>
> ... and reorder that paragraph to be first.

Sure.

-ritesh



[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [NTFS 3]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [NTFS 3]     [Samba]     [Device Mapper]     [CEPH Development]

  Powered by Linux