Date: Fri, 16 Oct 2015 13:16:39 -0600 From: Warner Losh <imp@bsdimp.com> To: Hans Petter Selasky <hp@selasky.org> Cc: Bruce Evans <brde@optusnet.com.au>, Warner Losh <imp@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r289405 - head/sys/ufs/ffs Message-ID: <C670A059-B35F-41F3-907A-F0937320CA6D@bsdimp.com> In-Reply-To: <5620B15C.8090104@selasky.org> References: <201510160306.t9G3622O049128@repo.freebsd.org> <20151016151349.W1280@besplex.bde.org> <5620B15C.8090104@selasky.org>
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[-- Attachment #1 --] > On Oct 16, 2015, at 2:12 AM, Hans Petter Selasky <hp@selasky.org> wrote: > > On 10/16/15 08:21, Bruce Evans wrote: >> In addition, making the file contiguous in LBA space doesn't >> improve the access times from flash devices because they have no seek >> time. > > Hi, > > This is not exactly true, like Bruce pointed out too. Maybe there should be a check, that if the block is too small reallocate it, else leave it for the sake of the flash. Doing 1K accesses versus 64K accesses will typically show up in the performance benchmark regardless of how fast the underlying medium is. But that’s not what this does. It isn’t the defrag code that takes the 2-8k fragments and squashes them into 16-64k block size for the device. This takes the larger blocks and makes sure they are next to each other. This takes large contiguous space (like 2MB) and puts as much as possible in a cylinder group. That’s totally useless on a flash drive. Since the sizes of the blocks are so large, moving them won’t change any benchmarks. Warner [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJWIU0XAAoJEGwc0Sh9sBEA2NAP/jExMKGTXDjVBkUPfavVpXSY cUdIspM7IEasio9YevjdT17MePqRGd5Iwc8ViYvZC2RwACUMYbjKl2fP02DxJfd2 BafqkQB+Ruxpgggj8YpV0J9o2vcagmehr9waX47DvlpQ+r1XnltmpK94xU3FP81F 4V2/7Cqqx0AA20yOD3dorEvZYEfV6w4fv1j0AqanXXzNOJ3uOY4G7XhTbDPr8eGg eOLeqocZ7ssN+Gms0VA8mUAK5nKld47bOJPM3M3+x3Q+GRxVQ0ojNQKHh8hBUlRN cLGL5SW0wTF4VpHAEx5MaC8YoWMhIvbFcf+rmFDTgfkeomE2eVSo5OdjbTQmdS/t yRGzjpRe/o20BSn0xURzkqwiIMKhoTzBeDOhyBP3WAmCy5P3JGsMCErsxTp3g0AM zEnA7d0AX79WfLxO+ybZyRFACO1W1N+0inlbB0QSouxIgqC85OJ2eohvQwexso1E MP+ZYpJXqiDsiEgt9r8Xy57yUbmS6Nyo5kkn6EutGozV+aQlZhgKaZtQl6KC7/1x fYvI4CFywfB/aVUQznaY3PGlDwd3123djNATTAI+z/dwX1P4R0elf2TfYlax0CBx aGY3PeExVZeclKD1eHYi/3ZlD37dzRs8Z7CZzd5OlXRHfvMZOMDi/lxswJZ2VcUh /UZAVvTW/OQ56aSejQhG =t5ja -----END PGP SIGNATURE-----
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