Revisiting 2.4.X __alloc_pages: X-order allocation failed

[Matthias Andree]

Hi,

I recently had troubles with excessively low I/O throughput when writing
a CD from an ISO image. The image file was on a reiserfs partition on an
IBM DCAS-32160 (USCSI), attached to an AHA2940Udontaskme (AIC7881U), the
writer is ATAPI 16x.  Pentium-II/400, 256 MB, PIIX4 IDE chip (BX chip
set I believe).  SuSE official 2.4.16 kernel as offered as update for
SuSE 7.3 -- I didn't check their patches, but their recent kernels were
based on -aa stuff AFAICS.

The low throughput showed in a big (16M) but empty (0 - 4%) cdrecord
FIFO, with the drive pausing during the write (didn't harm, burnproof
was on). 2400 kByte/s (for 16x CD writing) is far below the sustained
transfer rates which range from 4.7 at ID to 7.7 MB/s at OD.

This problem didn't show with vanilla 2.4.14.

I found a lot of __alloc_pages: X-order allocation failed in my logs,
with X from 1 to 3. Do these allocation failures impair I/O throughput
when reading stuff from a disk, tossing things through a
statically-allocated FIFO to a CD writer? If so, I might need to give
that box some other kernel.

-- 
Matthias Andree

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