Date: Tue, 30 Aug 2022 15:41:59 +0000 From: Rick Macklem <rmacklem@uoguelph.ca> To: Mateusz Guzik <mjguzik@gmail.com>, Alexander Motin <mav@FreeBSD.org>, Alan Somers <asomers@freebsd.org> Cc: "src-committers@FreeBSD.org" <src-committers@FreeBSD.org>, "dev-commits-src-all@FreeBSD.org" <dev-commits-src-all@FreeBSD.org>, "dev-commits-src-main@FreeBSD.org" <dev-commits-src-main@FreeBSD.org> Subject: Re: git: 35b7759c05cb - main - cp: Fix build without VM_AND_BUFFER_CACHE_SYNCHRONIZED. Message-ID: <YQXPR01MB415043ACC269C3256EAFB959DD799@YQXPR01MB4150.CANPRD01.PROD.OUTLOOK.COM> In-Reply-To: <CAGudoHEMRkBRT6ew9ROh1p-mmYCbkT%2BewuMdLTdUAiqwg=_3Og@mail.gmail.com> References: <202208301453.27UEroGr037461@gitrepo.freebsd.org> <CAGudoHEphH-4pKGf=ta4AWir2Uj9Mg_tUysU1V5ic6z_XVQG4Q@mail.gmail.com> <YQXPR01MB41500177CCDFEECFBE95861EDD799@YQXPR01MB4150.CANPRD01.PROD.OUTLOOK.COM> <837f27fc-97b0-6e71-50c0-12b8799e574d@FreeBSD.org> <CAGudoHEMRkBRT6ew9ROh1p-mmYCbkT%2BewuMdLTdUAiqwg=_3Og@mail.gmail.com>
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Mateusz Guzik <mjguzik@gmail.com> wrote: > On 8/30/22, Alexander Motin <mav@freebsd.org> wrote: >> On 30.08.2022 11:02, Rick Macklem wrote: >>> Mateusz Guzik <mjguzik@gmail.com> wrote: >>>> On 8/30/22, Alexander Motin <mav@freebsd.org> wrote: >>>>> The branch main has been updated by mav: >>>>> >>>>> URL: >>>>> https://cgit.FreeBSD.org/src/commit/?id=35b7759c05cbc65c06d87141da79f0f80af0f458 >>>>> >>>>> commit 35b7759c05cbc65c06d87141da79f0f80af0f458 >>>>> Author: Alexander Motin <mav@FreeBSD.org> >>>>> AuthorDate: 2022-08-30 14:51:21 +0000 >>>>> Commit: Alexander Motin <mav@FreeBSD.org> >>>>> CommitDate: 2022-08-30 14:51:21 +0000 >>>>> >>>>> cp: Fix build without VM_AND_BUFFER_CACHE_SYNCHRONIZED. >>>>> >>>>> It allows to not use mmap() for small files, which is not helpful >>>>> in case of ZFS. Should be no functional change. >>>>> >>>> >>>> This should be of no use thanks to copy_file_range >>> cp does not use copy_file_range(2) for small files, if I recall >>> correctly. >> >> Right. I tried to look for motivation, but history of this file goes >> back to 4.4 Lite. :) I wonder whether copy_file_range(2) for UFS does >> something clever, like this mmap() to avoid additional memory copy. It does not at this time. Unless both files are on the same file system and the file system provides a custom VOP_COPY_FILE_RANGE() { only NFS has one at this time }, it simply uses vn_rdwr() to do the file system I/O. A custom VOP_COPY_FILE_RANGE() can be implemented for file systems, if there is a better way for that file system. >> For >> ZFS though it cause big problem with buffer cache squeezing ARC to >> absolute minimum. So if there is agreement to modernize this, I'd >> completely support it. >> >> -- >> Alexander Motin >> > >The way I see it userspace cannot do it any faster. > >Especially with the zfs considerations it makes sense to straight up >copy_file_range if you can and let the kernel figure out what to do in >a sensible manner. Thought I have no idea if zfs is currently handled >in such a way. Someone(tm) should look into it. I've added asomers@, since he did the commit to cp so that it used copy_file_range(2) and left it doing small files using mmap(2). rick -- Mateusz Guzik <mjguzik gmail.com>help
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