linux-kernel - Re: [PATCH 08/13] IB/iser: set virt_boundary

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Date:   Wed, 5 Jun 2019 16:35:12 -0700
From:   Sagi Grimberg <sagi@...mberg.me>
To:     Jason Gunthorpe <jgg@...pe.ca>, Christoph Hellwig <hch@....de>
Cc:     Jens Axboe <axboe@...nel.dk>, Sebastian Ott <sebott@...ux.ibm.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Bart Van Assche <bvanassche@....org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Oliver Neukum <oneukum@...e.com>, linux-block@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-mmc@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-scsi@...r.kernel.org,
        megaraidlinux.pdl@...adcom.com, MPT-FusionLinux.pdl@...adcom.com,
        linux-hyperv@...r.kernel.org, linux-usb@...r.kernel.org,
        usb-storage@...ts.one-eyed-alien.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/13] IB/iser: set virt_boundary_mask in the scsi host


>> This ensures all proper DMA layer handling is taken care of by the
>> SCSI midlayer.
> 
> Maybe not entirely related to this series, but it looks like the SCSI
> layer is changing the device global dma_set_max_seg_size() - at least
> in RDMA the dma device is being shared between many users, so we
> really don't want SCSI to make this value smaller.
> 
> Can we do something about this?

srp seems to do the right thing:
target_host->max_segment_size = ib_dma_max_seg_size(ibdev);

But iser does not, which means that scsi limits it to:
BLK_MAX_SEGMENT_SIZE (64k)

I can send a fix to iser.

> Wondering about other values too, and the interaction with the new
> combining stuff in umem.c

The only other values AFAICT is the dma_boundary that rdma llds don't
set...