per-queue bioset is used originally for avoiding deadlock, are you
sure the static bioset is safe?
Can you explain this? I didn't find any indication of that in the change
log history...
Originally introduced by Kent:
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commit 54efd50bfd873e2dbf784e0b21a8027ba4299a3e
Author: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Date: Thu Apr 23 22:37:18 2015 -0700
block: make generic_make_request handle arbitrarily sized bios
The way the block layer is currently written, it goes to great lengths
to avoid having to split bios; upper layer code (such as
bio_add_page())
checks what the underlying device can handle and tries to always create
bios that don't need to be split.
But this approach becomes unwieldy and eventually breaks down with
stacked devices and devices with dynamic limits, and it adds a lot of
complexity. If the block layer could split bios as needed, we could
eliminate a lot of complexity elsewhere - particularly in stacked
drivers. Code that creates bios can then create whatever size bios are
convenient, and more importantly stacked drivers don't have to deal
with
both their own bio size limitations and the limitations of the
(potentially multiple) devices underneath them. In the future this
will
let us delete merge_bvec_fn and a bunch of other code.
We do this by adding calls to blk_queue_split() to the various
make_request functions that need it - a few can already handle
arbitrary
size bios. Note that we add the call _after_ any call to
blk_queue_bounce(); this means that blk_queue_split() and
blk_recalc_rq_segments() don't need to be concerned with bouncing
affecting segment merging.
Some make_request_fn() callbacks were simple enough to audit and verify
they don't need blk_queue_split() calls. The skipped ones are:
* nfhd_make_request (arch/m68k/emu/nfblock.c)
* axon_ram_make_request (arch/powerpc/sysdev/axonram.c)
* simdisk_make_request (arch/xtensa/platforms/iss/simdisk.c)
* brd_make_request (ramdisk - drivers/block/brd.c)
* mtip_submit_request (drivers/block/mtip32xx/mtip32xx.c)
* loop_make_request
* null_queue_bio
* bcache's make_request fns
Some others are almost certainly safe to remove now, but will be left
for future patches.
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